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EVOLVING TECHNOLOGIES FOR 3G CELLULAR
WIRELESS COMMUNICATIONS SYSTEMS
CDMA2000 1xEV-DO Revision A:
A Physical Layer and MAC Layer Overview
Naga Bhushan, Chris Lott, Peter Black, Rashid Attar, Yu-Cheun Jou, Mingxi Fan, Donna Ghosh, and
Jean Au, QUALCOMM, Inc.
ABSTRACT
®
CDMA2000 is a registered trademark of the
Third Generation Partnership Project 2 (3GPP2).
1
A flow is a source with
transmission requirements
associated with an application such as video telephony, voice over IP
(VoIP), gaming, Web
browsing, and file transfer.
2
There are over 16 million 1xEV-DO Revision 0
users as of September
2005.
3
TIA is the Telecommunications Industry Association of North America.
This article presents key enhancements to
CDMA2000 1xEV-DO systems embodied in
1xEV-DO Revision A. These enhancements provide significant gains in spectral efficiency and
substantial improvements in QoS support relative to 1xEV-DO Revision 0. In particular,
1xEV-DO Revision A approximately doubles the
uplink spectral efficiency and doubles the number of terminals with delay-sensitive applications
that can be simultaneously supported on the system. It provides substantial reduction in latencies (approximately 50 percent) during both
connection setup and the connected state. It
offers comprehensive network control over terminal and application performance to enable the
desired trade-offs between capacity and latency/
fairness, thereby providing full QoS support and
enhanced user experience. It also provides coverage improvement (approximately 1.5 dB) relative to 1xEV-DO Revision 0. This enables
operators to offer services such as VoIP, video
telephony, mobile network gaming, push-to-talk,
Web browsing, file transfer, and video on
demand to a larger number of simultaneous
users. The 1xEV-DO Revision A network can
provide downlink sector capacity of 1500 kb/s
and uplink capacity of 500 kb/s (two-way receive
diversity) or 1200 kb/s (four-way receive diversity) with 16 active users per sector, using just 1.25
MHz of the spectrum.
INTRODUCTION
CDMA2000 ® 1xEV-DO Revision 0 (also
referred to as DO Rev 0) was driven by the
design vision of a “wide-area-mobile wireless
Ethernet” as described in [1]. The result was a
high-rate wireless packet data system with substantial improvement in downlink capacity [2]
and coverage over traditional CDMA2000 systems such as IS-95 and IS-2000. In addition to
high throughput, DO Rev 0 provides quality of
service (QoS) support to enable operators to
offer a variety of applications with different
IEEE Communications Magazine • February 2006
throughput and latency requirements. These
improvements were accomplished through the
use of large packet sizes encoded with low-rate
turbo codes, transmitted using adaptive modulation and coding, downlink physical layer hybrid
automatic repeat request (H-ARQ), and downlink multi-user diversity, together with antenna
diversity at the receiver. DO Rev 0 systems support per flow1 QoS on the downlink and per terminal QoS on the uplink.
Increasing demand for high-speed wireless
Internet access has resulted in rapid growth of
the number of CDMA2000 1xEV-DO users
worldwide. 2 Operators have observed a strong
demand for applications such as VoIP, video
telephony, wireless gaming, and push-to-talk
(PTT), along with demand for downlink-intensive applications such as Web browsing and file
transfer. These applications demand a system
that can support large numbers of simultaneous
users while meeting their desired latency requirements. In order to meet this demand, 3GPP2
approved enhancements to CDMA2000 1xEVDO Revision 0 (TIA-856). The CDMA2000
1xEV-DO Revision A system (TIA-856-A) was
therefore standardized in March 2004 by 3GPP2
and TIA.3
We provide a summary of 1xEV-DO Revision 0 and highlights of 1xEV-DO Revision A. A
detailed discussion of the enhancements to connection setup is presented. We provide a detailed
discussion of the enhancements to the uplink
and downlink, respectively. We provide a performance summary followed by conclusions.
1XEV-DO SALIENT FEATURES
1XEV-DO REVISION 0
As in IS-95 and IS-2000 systems, the 1xEV-DO
Revision 0 carriers are allocated 1.25 MHz bandwidth and use a direct sequence (DS) spread
waveform at 1.2288 Mchips/s. The fundamental
timing unit for downlink transmissions is a
1.666... ms slot that contains the pilot and medium access control (MAC) channels, and a data
0163-6804/06/$20.00 © 2006 IEEE
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1/2 slot
1024 chips
Data
400
chips
MAC
64
chips
Pilot
96
chips
1/2 slot
1024 chips
MAC
64
chips
Data
400
chips
Data
400
chips
MAC
64
chips
Pilot
96
chips
MAC
64
chips
Data
400
chips
Active slot
n Figure 1. 1xEV-DO downlink slot structure.
4
A three-slot separation
between subpacket transmissions allows the AT
time to demodulate and
decode the packet, and
indicate to the access network whether or not the
packet was successfully
decoded.
5
Bi-orthogonal sequences
are chosen for the preamble due to better distance
properties than orthogonal
codes. In addition, shorter
Walsh sequences better
preserve orthogonality in
fading.
76
portion that may contain the traffic or control
channel as shown in Fig. 1. Unlike IS-2000,
where a frame is 20 ms, a frame in 1xEV-DO
Revision 0 is 26.66... ms.
The pilot channel is transmitted at full power
for 96 chips every half-slot (each slot is composed of 2048 chips), providing not only a reference for coherent demodulation of traffic and
MAC channels but also a 1200 Hz sampling of
the channel state. These samples are used to
estimate and predict the received signal-to-interference-and-noise ratio (SINR) at the access terminal (AT) in the near future, which aids the
terminal in determining the maximum data rate
that can be supported on its downlink. This provides the system with a mechanism for fast adaptation of modulation and coding schemes to
different mobile channel environments.
The MAC channel consists of a reverse activity (RA) channel and reverse power control
(RPC) channel. The RA channel from a particular sector provides a 1-bit feedback to all terminals that can receive that sector’s forward link
indicating whether or not its uplink load exceeds
a threshold. The RPC channels from a particular
sector carry a unique 1-bit closed loop power
control command (update rate of 600 Hz) for
each of the access terminals that include that
particular sector in their active set. The data rate
control (DRC) lock channel is punctured into
the RPC channel and is used to indicate the
channel state from the access terminal to the
access network.
1xEV-DO Revision 0 uses a time-division
multiplexed (TDM) downlink (transmit to one
user at a time). The traffic channel data rate
used by the access network for transmission to an
access terminal is determined by the DRC message previously sent by the access terminal on the
uplink. The DRC indicates not only the data rate
but also the modulation, code rate, preamble
length, and maximum number of slots required
to achieve the desired physical layer error rate.
1xEV-DO Revision 0 introduced physical
layer H-ARQ on the downlink. The access network transmits packets to an access terminal
over multiple slots staggered in time.4
At higher SINR, significant coding gains are
achieved by incremental transmission of parity
bits, and at lower SINR, powerful coding is
achieved by simple repetition of a rate 1/5 turbo
encoded packet.
The 1xEV-DO Revision 0 downlink traffic
channel is a shared medium that provides highpeak-rate transmissions to active access terminals. Addressing on the shared channel is
achieved by a MAC index that is used to identify
data transmissions from a sector to a particular
access terminal. The packet preamble is covered
with a bi-orthogonal sequence 5 determined by
the MAC index assigned to the access terminal.
In order to maximize performance in a variety of
channel conditions, three basic mechanisms exist
to control access to the downlink traffic channel.
Open-loop rate control: A DRC message is
sent by all ATs containing a requested data rate
and a transmitting sector indication. The transmitting sector chosen by the AT is the one that
provides the best downlink channel and can
receive the a priori downlink channel state information (CSI) with acceptable reliability.
Adaptive data scheduler: This takes into
account fairness, queue sizes, and the most
recent a priori downlink CSI provided by the
DRCs. While the specification does not specify
the details of the scheduler, some form of proportional-fairness scheduler [2] is typically used,
so as to exploit multi-user diversity on the downlink.
Closed-loop rate control: A fast feedback
acknowledgment (ACK) channel allows the data
rate of a packet to be effectively increased
beyond the data rate corresponding to the
requested DRC if the channel conditions experienced by the transmission to the AT improve
relative to the channel estimate used to generate
the DRC.
A combination of H-ARQ and multi-user
diversity improves performance in a variety of
channel conditions; the former provides capacity
gains in fast-fading channels, the latter in slowfading channels [3].
The uplink in 1xEV-DO Revision 0 is similar
to that in IS-2000 with some key differences:
• Stochastic distributed rate control with
direct measurement of sector loading via
rise-over-thermal (RoT) measurement
defined as Io/No, where Io is the total
received power and No is the thermal noise
floor. This is enabled by the introduction of
a silence interval when all terminals in the
system do not transmit, enabling the access
network to measure no.
• Explicit uplink rate indication using the
reverse rate indication (RRI) channel.
• Closed-loop power control of the pilot channel, with gains for the data and overhead
channels specified relative to the pilot. The
traffic-to-pilot power ratios are selected
such that the pilot SINR is not a function
of the data rates and therefore does not
require adjustment at rate transitions.
IEEE Communications Magazine • February 2006
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The uplink MAC channel protocol employs a
distributed algorithm subject to feedback control
and defines the rules used by each AT for data
transmissions. The AT receives a reverse activity
(RA) bit from each sector in its active set indicating whether or not the RoT exceeds a predetermined threshold. This information determines
whether the ATs increase or decrease their data
rates. The AT also receives an explicit rate limit
message indicating the maximum data rate at
which it may transmit. The access network provides each AT with two rate transition probability vectors the ATs use to increase or decrease
data rate, respectively, depending on the effective RA bit (logical OR of RA bits from all sectors in the active set), available data, and power
amplifier (PA) headroom. The rate transition
vectors specify the probability that the AT will
increase or decrease its uplink data rate based
on the current data rate and effective sector
loading.
1XEV-DO REVISION A
The salient enhancements offered by
CDMA2000 1xEV-DO Revision A are:
• An uplink physical layer with H-ARQ, higher-order modulation (quadrature phase
shift keying [QPSK] and 8-PSK), higher
peak rate (1.8 Mb/s), and finer rate quantization.
• An uplink multiflow MAC with QoS support, comprehensive network control of
spectral efficiency and latency trade-off for
each application flow, and a more robust
interference control mechanism that permits system operation at higher load.
• A downlink physical layer with higher peak
rate (3.1 Mb/s), finer rate quantization, and
short packets for transmit delay reduction
and improved link utilization.
• A downlink MAC layer that permits the
access network to serve multiple users with
the same physical layer packet, improving
not only transmission latency but also packing efficiency. The transmission latencies
are further improved by seamless adaptive
server selection and service to users reporting null-rate DRCs.
• Rapid connection setup for applications
that require “instant connect” via use of
shorter interpacket intervals and a higherrate access channel.
CONNECTION SETUP
CONTROL CHANNEL
The control channel in 1xEV-DO Revision 0 is
used for transmission of control and signaling
information on the downlink. Two types of
control channels, synchronous control (SC) and
asynchronous control (AC), are supported. The
former is transmitted once every 256 slots
(426.66... ms) and the latter whenever needed
but not overlapping with the SC. The AC may
be used to transmit delay-sensitive signaling
information to ATs that either have an active
connection with the access network already, or
are trying to establish an active connection.
For example, once the access network decodes
an access probe from an AT, AC may be used
IEEE Communications Magazine • February 2006
to send an acknowledgment to the access terminal. On the other hand, using SC to send
pages incurs large delays, because SC transmissions are rather infrequent. Moreover, SC and
AC are transmitted at 38.4 kb/s (16-slot duration) or 76.8 kb/s (8-slot duration) using a
1024-bit payload to ensure high coverage for
the control channel. However, this results in
poor packing efficiency and inefficient utilization of downlink resources when transmitting a
page 6 (typically 128 bits of data) to an AT
using the SC.
In order to allow the ATs to get quick access
to the system while maintaining long terminal
standby time and ensuring efficient use of downlink resources, the following enhancements were
introduced for the control channel in 1xEV-DO
Revision A:
• Subsynchronous control channel (SSC)
transmitted synchronously with shorter
intertransmit duration relative to the SC
• Use of short physical layer packets (128,
256, or 512 bits) for transmitting SSC and
AC to ATs that do not have an active connection with the access network
The minimum intertransmit interval for the SSC
packets may be as low as four slots.
A page arriving at the access network
between two SC packet transmissions is not
transmitted until the next SC in DO Rev 0 but is
transmitted using the next SSC (64-slot SSC
interval) in DO Rev A. In addition, the page
transmission and access ACK take a maximum
of just four slots each in DO Rev A, due to the
use of smaller payload sizes (128, 256, or 512
bits). DO Rev A also allows grouping of users
that listen for SSC at certain time instants, thereby further improving terminal standby time.
The control channel
in 1xEV-DO Revision
0 is used for
transmission of
control and signaling
information on the
downlink. Two types
of control channels,
synchronous control
(SC) and
asynchronous
control (AC), are
supported.
ACCESS CHANNEL
Key access channel enhancements in DO Rev A
are:
• Reduced access channel connection setup
time
–Higher-rate access channel (up to 38.4
kb/s)
–Shorter access channel preamble (4 instead
of 16 slots)
–Reduced intrasequence interprobe latency
• Dynamic adjustment of access channel
transmit power level
• Initial probe power adjusted based on forward link pilot strength to achieve desired
probe success rate and minimize network
interference
• Network control over access channel performance
–Access probe success rate adaptation via
network adaptive OpenLoopAdjust
–Network control over the maximum access
channel data rate and maximum payload
size per terminal
DO Rev A access terminals may transmit
(access network controlled) on the access channel at up to 38.4 kb/s subject to data and power
constraints, while in DO Rev 0 the access channel data rate is restricted to 9.6 kb/s. The amount
of data that the access terminal is permitted to
transmit on the access channel is also access network controlled.
6
A Message sent by an
access network to an AT
instructing the AT to set
up a traffic channel.
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Since the open loop
turnaround
Page 78
P-ARQ bit or
ARQ channel
OpenLoopAdjust, is
generated based on
ACK
1.5 subframe
parameter,
L-ARQ bit or
ARQ channel
some assumptions of
ACK
1.5 subframe
3 slots
channel conditions
and sector loading,
the access probe
H-ARQ bit or
ARQ channel
NAK
success rate may
NAK
NAK
First subpacket
for the next
physical layer
packet
transmission
be different than
desired, resulting in
either unacceptable
Access Channel
latencies or
undesired uplink
interference.
Reverse traffic
channel physical
layer packet
transmissions
Subframes
Transmit
subpacket
1
n
Transmit
sub-packet2
PHYSICAL LAYER
78
Transmit
subpacket
1
n Figure 2. Example of normal packet termination (16-slot latency target7).
UPLINK
The latency target is
defined as the number of
slots of transmission
required to achieve the
desired packet error rate
(PER, typically 1 percent)
regardless of channel conditions.
Transmit
subpacket
4
n + 1 n + 2 n + 3 n + 4 n + 5 n + 6 n + 7 n + 8 n + 9 n + 10 n + 11 n + 12
In addition to a higher data rate on the initial
access probe, DO Rev A allows the access network to specify the interprobe latency (within an
access probe sequence). Therefore, DO Rev A
can achieve significant reduction in reverse link
access latency.
The access channel transmit power is a function
of the total received power on the forward link and
the open loop turnaround parameter. If the OpenLoopAdjust is designed based on cell edge assumptions, ATs closer to the cell center would transmit
more power than necessary (the access probes
directed to the sector with the best forward link).
DO Rev A therefore provides the ATs a mechanism to adjust the transmit power level as a function of the forward link pilot strength of the sector
to which the access probe is directed.
Since the open loop turnaround parameter,
OpenLoopAdjust, is generated based on some
assumptions of channel conditions and sector loading, the access probe success rate may be different
than desired, resulting in either unacceptable
access channel latencies or undesired uplink interference. Access terminals in DO Rev A include the
probe number (within a sequence) in the probe
transmission that permits the access network to
determine the access probe success probability distribution and adapt OpenLoopAdjust to achieve
the desired latencies on the access channel.
7
Transmit
subpacket
3
Key physical layer enhancements to the DO Rev
A uplink are:
• Physical layer H-ARQ and support for
MAC layer ARQ
• Higher data rates (peak data rate of 1.8
Mb/s) and finer rate quantization
• Higher order modulation that allows the
use of low-rate turbo codes at high data
rates and large payload sizes
Hybrid ARQ — Substantial gains in downlink
capacity were achieved in DO Rev 0 due to the
use of physical layer H-ARQ [4]. DO Rev A
introduces H-ARQ on the uplink in order to
exploit the excess E b /N 0 due to power control
imperfections and channel variations.
With H-ARQ, the uplink packet transmissions are staggered in time to allow the access
network to demodulate and decode the packets
and then transmit an ACK to the AT indicating
whether or not the transmitted packet was
decoded. As shown in Fig. 2, each physical layer
packet is sent using one or more four-slot subpackets (maximum of four subpackets). There
are eight slots between successive transmissions
of the subpackets of the same physical packet,
which can be used for transmissions of other
packets (total of three interlaces).
Figure 2 shows the ARQ mechanism for a
packet transmitted over all four subpackets. In
this example the access network transmits negative ACK (NAK) responses on the ARQ channel
using the H-ARQ bit after the first three subpackets are transmitted by the access terminal.
After the fourth subpacket, the sector transmits
an ACK using the last ARQ (L-ARQ) and packet ARQ (P-ARQ) bits indicating that the sector
successfully received the packet. The L-ARQ and
P-ARQ bits are used to support MAC layer
ARQ which will be described later in this section.
The ARQ channel (to convey ACKs for
uplink transmissions) is carried on the forward
MAC channel, which is limited to 256 chips/slot.
The additional overhead of the ARQ channels is
accommodated by reducing the power control
overhead, achieved by lowering the closed loop
power control update rate to 150 Hz for DO
Rev A terminals (from 600 Hz for DO Rev 0).
This enables transmission of ARQ, RPC, and
DRC lock channels for large numbers of simultaneous users without increasing the total MAC
overhead.
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Physical Layer Structure — Figure 5 shows
physical layer channels in DO Rev A with the
channels new to DO Rev A and the modified
channels shown in addition to the uplink physical layer subframe structure. The ACK and DSC
channels are TDM. The pilot, RRI, ACK/DSC,
DRC, data, and auxiliary pilot channels are
orthogonally spread by Walsh functions of length
2, 4, 8, 16, or 32. Each AT uses the DSC channel
to provide the access network with an early indication of the exact instant of time at which the
change in downlink server takes place. The
reverse link capacity impact due to the DSC
channel is minimized as it is transmitted at a low
gain relative to reverse link pilot (–15.5 dB for
active cell size of one and –9 dB for active cell
size larger than one) as it is transmitted over
several slots (typically 64). The auxiliary pilot
channel is used to provide reverse link channel
estimation for the large reverse link physical
layer packets.
Physical Layer Modulation — The DO Rev A
uplink supports higher-order modulation8 (i.e.,
QPSK and 8-PSK), and each modulated data
stream is covered by either a quaternary or binary Walsh function. The modulation types supported by the DO Rev A uplink are B4 (BPSK
modulation with quaternary Walsh cover), Q4
(QPSK modulation with quaternary Walsh
cover), Q2 (QPSK modulation with binary Walsh
cover), Q4Q2 (sum of the Q4 and Q2 modulated
symbols), and E4E2 (sum of E4 [8-PSK modulation with quaternary Walsh covers] and E2 [8PSK modulation with binary Walsh covers]
modulated symbols).
The use of higher order modulation (QPSK
and 8-PSK), and introduction of the binary
Walsh cover and Q4Q2 and E4E2 modulation
types result in more efficient use of the bandwidth, which significantly improves the code
rates for medium and high data rates. In DO
Rev A data rates up to 307.2 kb/s can all be
transmitted with rate 1/5 turbo code [6], whereas
in DO Rev 0 the 153.6 kb/s data rate could only
IEEE Communications Magazine • February 2006
Impact of decimated power control + H-ARQ on Ecp/Nt
–19
Ecp/Nt (dB)
Figure 3 shows the impact of the reduced
closed power control update rate on the pilot
channel signal-to-noise ratio (E c/N t). With the
exception of channel model A [5], we see that
the Pilot E c/N t with 150 Hz closed loop power
control and interlacing is lower than that with
600 Hz power control. More important, the
combination of 150 Hz closed loop power control and H-ARQ results in total required Eb/N0
(after early termination) that is substantially
lower (by 2 to 3 dB) than DO Rev 0, across all
channel conditions. These gains are corroborated by the early termination statistics under various channel conditions and latency targets
shown in Fig. 4. Figure 4 shows the early termination probabilities for the different channel
models for 16-slot and 8-slot latency targets
after 4, 8, and 12 slots. The 8-slot early termination probabilities include the termination after 4
slots, and the 12-slot early termination probabilities include termination after 4 and 8 slots.
Physical layer ARQ also results in an uplink
coverage improvement of 1.5 dB for a nominal
data rate of 9.6 kb/s.
–20
–32
–22
1xEV-DO revision 0
1xEV-DO revision A
1
2
3
Channel model
5
4
Impact of decimated power control + H-ARQ on Eb/Nt
5
Eb/Nt (dB)
12:12 PM
1xEV-DO revision 0
1xEV-DO revision A
4
3
2
1
1
2
3
Channel model
5
4
n Figure 3. Received pilot Ecp/Nt and total Eb/Nt vs. channel condition for a
256-bit packet transmission (DO Rev 0 vs. DO Rev A).
Early termination probabilities, 256-bit payload, 16-slot LT
100
Percentage
1/24/06
4-slot
8-slot
12-slot
50
0
A
B
C
D
E
Channel models
Mix
Early termination probabilities, 256-bit payload, 8-slot LT
100
Percentage
BHUSHAN LAYOUT
4-slot
50
0
A
B
C
D
Channel models
E
Mix
n Figure 4. Uplink physical layer packet early termination probability.
be sent using rate 1/2 code due to the use of
BPSK modulation.
The DO Rev A uplink supports data rates
from 4.8 kb/s to 1.8432 Mb/s and payload sizes
ranging from 256 to 12,288 bits. It allows the
access network to set two latency targets for
each payload size for the AT. The latency target
is defined by one of two transmission modes, low
latency (LoLat) and high capacity (HiCap). The
former uses less than four subpackets (16 slots)
to transmit the packet, and the latter typically
uses four subpackets. The payload sizes and
latency targets from which the access network
8
DO Rev 0 uplink supports BPSK modulation
with quaternary Walsh
covering for data rates up
to 153.6 kb/s.
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The DO Rev A uplink
Reverse
supports data rates
from 4.8 kb/s to
1.8432 Mb/s and
Access
Traffic
payload sizes ranging
from 256 to 12,288
bits. It allows the
Pilot
Data
access network to
Primary
pilot
Auxiliary
pilot
Medium
access
control
ACK
Reverse
rate
indicator
Data
rate
control
Data
source
control
Data
set two latency
targets for each
payload size for the
access terminal.
RRI
The latency target is
defined by one of
Data channel
two transmission
modes, low latency
(LoLat) and high
DRC channel
ACK
DSC
capacity (HiCap).
ACK
DSC
ACK
DSC
ACK
DSC
Auxiliary pilot channel
Pilot channel
1 subframe
1 slot
n Figure 5. 1xEV-DO Revision A uplink physical layer channels and subframe structure.
and AT can choose are listed in [6], with packet
transmission latencies in the range of 6.66–66.66
ms, as desired by the application.
9
The nominal data rate is
the data rate achieved
after transmission of the
number of subframes as
specified by the latency
target.
10
The T2P profile is set
per AT for each payload
size and transmission
mode. A T2P profile is an
ordered set of T2P values
that the AT is required to
use for each subpacket
transmission.
80
Capacity and Latency Trade-Off — Due to
physical layer H-ARQ in DO Rev A and latency
control, nominal9 data rate is no longer an accurate indicator of the system resources used (or
the interference caused to the system) by an AT
or a flow of an AT. Unlike DO Rev 0 where all
data rates have a fixed latency target (i.e., 16
slots), each data rate in DO Rev A is specified
by payload size and latency target. For example,
9.6 kb/s can be achieved by a 256-bit packet
transmitted over 16 slots or a 128-bit packet
transmitted over 8 slots. Packet transmissions
with shorter latency targets have less time diversity and fewer ARQ rounds, and are hence more
susceptible to channel variations. The lowerlatency transmissions therefore require a larger
traffic-to-pilot power ratio (T2P, i.e., system
resource) to achieve the same error performance
at the latency target as higher-latency transmissions of the same data rate.
The AT can transmit each physical layer
packet using one of two transmission modes,
LoLat or HiCap. Packets transmitted in LoLat
mode are power-boosted (transmitted with a
higher T2P) to ensure termination within the
latency target. The access network assigns an
AT-specific T2P profile10 for each payload size
for both transmission modes. If packets of a
LoLat transmission mode fail to decode by the
latency target, the AT continues transmission
until the packet is successfully decoded or a total
of four subpackets have been transmitted. Given
a target packet error rate (PER) of 1 percent at
the latency target, this achieves a sub-1 percent
physical layer PER, which improves the performance of higher-layer protocols. For a given
T2P allocation, the AT can trade off between
capacity and latency (i.e., achieving high capacity
using a large payload or low latency with a smaller payload).
System Operation at High Rise-over-Thermal — System operation at high RoT may lead
to power control instability in code-division multiple access (CDMA) systems, as small changes
in load at high operating points result in large
variations in RoT. For example, with a load of
0.7, the RoT equals 5 dB with other cell interference factor of 0.2. However, if the other-cell
interference is changed to 0.4, the RoT exceeds
20 dB. The changes in load or other cell interference may be triggered by changes in transmission data rate or power control imperfections.
Use of direct RoT measurement allows operation of DO Rev 0 systems at high RoT without
compromising system stability. System stability at
higher RoT can be further improved by reducing
the delay in the RoT control loop. This is
achieved in DO Rev A by the use of a quick
reverse activity bit (QRAB). The Reverse Activity (RA) bit is updated every slot (1.66... ms) in
DO Rev A instead of per-frame (26.66... ms) as
in DO Rev 0. Due to the reduced delay of the
RoT control loop the DO Rev A system can
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operate at the same average RoT (5 dB in this
case) as that of a DO Rev 0 system with significantly increased stability. Alternatively, it can
operate at a notably higher RoT (higher RoT
implies higher sector capacity) with the same
stability as that of a DO Rev 0 system. Note that
the overhead channel performance is unaffected
as long as the AT can close the uplink, since the
desired pilot SINR is maintained by power control, and all overhead channel gains are fixed
relative to the pilot.
MAC Layer ARQ — In order to reduce the
PER seen by the upper layers, it is desirable to
recover physical layer packet errors through a
MAC layer ARQ mechanism with quick turnaround. DO Rev A allows the AT to retransmit
the MAC layer payload contained in a packet
that fails to decode even after 16 slots of transmission. MAC layer retransmission is triggered
by the L-ARQ and/or P-ARQ bits that are
received within 12 subframes of the start of
packet transmission.
MEDIUM ACCESS CONTROL LAYER
Key enhancements to the uplink traffic channel
MAC in DO Rev A are:
• Comprehensive centralized control with
minimal signaling overhead
• Unified approach to intra-AT QoS and
inter-AT QoS
• Adaptive token bucket access control
• Multiflow MAC with per flow QoS control
with explicit capacity, latency, and fairness
trade-off per flow
• RoT-sensitive per flow T2P allocation
Comprehensive Centralized Control —
1xEV-DO Revision A provides the access network several mechanisms for centralized control
in addition to those provided in 1xEV-DO Revision 0. 1xEV-DO Revision A adopts a flow-oriented QoS approach. It achieves precise control
of access terminal resource allocation with centralized resource allocation by the access network and distributed rate selection at the access
terminal. The access network determines the
long-term resource allocation for each flow in
the network, while the AT controls the time-critical allocation (for each physical layer packet)
based on the rules specified by the access network, in conjunction with local information
about queue buildup and packet delay. This twosided control philosophy minimizes signaling
overhead as well as delays in physical layer allocations. The AT executes the multiflow MAC
algorithm using parameters downloaded from
the access network, thereby synthesizing the
resource allocation desired by the access network. In this framework each AT may be visualized as a state machine whose behavior is
controlled by the access network. DO Rev A
also defines request and grant messages for
resource allocation, which may be regarded as
an explicit mechanism to force the AT state
machine to a desired state from time to time.
In DO Rev A, the T2P is treated as a sector
resource, and the uplink MAC specifies rules for
mapping the continuous-valued allocation of the
T2P resource into discrete-valued transmit T2P
IEEE Communications Magazine • February 2006
(TxT2P) corresponding to a physical layer packet transmission. The centralized control mechanisms in DO Rev A are:
• Per-flow QoS control: Each flow is assigned
a LoLat or HiCap attribute, which indicates
the preferred transmission mode for data
associated with that flow.
• Fast RA bit control: Per-slot update of RA
bit.
• Max per AT TxT2P control: The access network can control the maximum TxT2P that
each AT can use for uplink traffic channel
transmissions.
• Latency shaping: By appropriate choice of
TxT2P value for transmission of each payload in each transmission mode, the access
network can control the latency characteristics of each AT.
• Flow adaptive PER: Assignment of a transmission mode (i.e., LoLat or HiCap) to a
flow determines the physical layer PER for
packet transmissions of each flow.
• Flow-specific interpretation of sector loading: While ATs typically use an “OR of the
BUSY” rule to determine the effective RA
bit, the access network can allow selected
flows to modify the rule.
• HiCap flow to LoLat conversion: The access
network specifies rules using which a HiCap
flow can be transmitted in LoLat mode
based on network loading and flow QoS
requirements.
• Explicit request and grant: In addition to
the centralized resource allocation with distributed rate selection, DO Rev A supports
changing MAC flow parameters and state
using an explicit request and grant mechanism.
• Explicit capacity/fairness/interference control: DO Rev A allows the access network
to explicitly trade off capacity, fairness, and
latency among active flows in addition to
limiting interference among flows.
We next discuss the explicit request and grant
mechanisms. The access network can impose
conditions on whether or not the AT is required
to transmit the request messages and the frequency at which it is required to transmit them.
The request messages indicate the PA headroom
estimate and the queue length for MAC flows
for which the AT requests an explicit resource
assignment. The grant messages are optionally
transmitted (i.e., not coupled with the request
messages) by the access network and contain the
T2PInflow, duration for maintaining the T2PInflow (resource allocation) constant, and the
token bucket level per flow. The T2P grants are
resource allocations based on network loading
dynamics, and not per packet allocations. The
time-critical events are handled directly at the
AT. The use of the explicit request and grant
messages allows a seamless transition between
the allocation based on a distributed rate selection and centralized resource allocation, and a
direct centralized allocation for the desired
flows. Each flow seamlessly converges to its
long-term allocation as specified by the access
network once the duration for which the T2PInflow allocation is frozen expires. Use of the
explicit request and grant messages allows faster
DO Rev A allows the
AT to retransmit the
MAC layer payload
contained in a
packet that fails
to decode even
after 16 slots of
transmission. MAC
layer retransmission
is triggered by the
L-ARQ and/or P-ARQ
bits that are received
within 12 subframes
of the start of packet
transmission.
81
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T2PInflow =
new resource
inflow (mean
T2P resource
based on AN
assigned flow
priority)
BucketLevel =
unused
accumulated
resource
BucketLevelSat =
maximum
allowed
bucket size
T2P = uplink
MAC resource
PotentialOutflow = maximum
allowed resource withdrawal
Data
Physical
layer
packet
TxT2P Outflow = actual
T2P withdrawal from
the bucket
n Figure 6. Token-bucket-based access control (DO Rev A).
convergence to the desired resource allocation
and aids in QoS enforcement and policing.
Unified Approach to QoS — The DO Rev 0
MAC supports only a single uplink MAC flow
per AT. In other words, there is no differentiation of packets from different applications with
distinct QoS requirements. The DO Rev A
uplink MAC enables intra-user QoS. Packets
from latency-sensitive flows that arrive at the
access terminal following a large packet for
delay-tolerant flow are transmitted using the first
MAC packet by an intra-AT QoS aware (multiflow) MAC in contrast to the operation of an
intra-AT QoS unaware (single-flow) MAC where
packets are transmitted in order of arrival, which
results in higher and unpredictable latency and
jitter — both undesirable for real-time multimedia applications.
The DO Rev A uplink MAC algorithm specifies the behavior of each MAC flow in addition
to the AT behavior as specified in DO Rev 0.
The DO Rev 0 approach relies on AT implementations to appropriately allocate resources
among the applications, whereas the DO Rev A
approach allows access network direct control
over behavior of each flow. The DO Rev 0
approach requires renegotiation of assigned rate
transition probabilities each time the nature or
composition of the constituent flows at the AT
changes. The DO Rev A MAC uses a unified
approach to inter-AT QoS and intra-AT QoS,
and decouples flow behavior from its location, so
flows with the same MAC parameters achieve
the same performance irrespective of whether
residing at a given AT or across multiple ATs
(subject to power and system load constraints).
Adaptive Token Bucket Access Control —
The DO Rev A uplink MAC uses an adaptive
token bucket access control per flow with T2PInflow as the adaptation parameter, as shown in
Fig. 6. This allows a restriction to be imposed on
the source behavior and the contribution of each
flow to the sector RoT to be controlled. With
this mechanism the AT appears as a token bucket regulator to the rest of the network. A token
82
bucket is defined for each uplink traffic channel
MAC flow and represents the stored T2P
resource. Control of the token bucket and other
MAC parameters enables access network control
of the transmitted T2PInflow. The token bucket
allows smoothing of T2PInflow allocation when
interarrival time between higher layer packets is
short. With appropriate parameter settings, the
access network can also grant an AT the ability
to handle bursty sources (i.e., high peak-to-average throughput) with well-defined restrictions on
the peak-to-average ratio of the TxT2P. The
token bucket is filled each subframe with T2PInflow and emptied by the actual TxT2P allocation
for a physical layer packet transmission. Figure 7
shows a comparison of the throughput and bit
delay between DO Rev 0 and DO Rev A using a
temporal trace. For the example presented here,
both systems use the default settings — the
default rate transition probabilities for DO Rev
0 and the default MAC parameters for DO Rev
A. It can be seen that the flow throughput for
DO Rev A is nearly constant, while in DO Rev 0
it suffers from startup effects due to the rate
transition probabilities and a startup data rate of
9.6 kb/s. The bit delay for DO Rev A is low and
constant, leading to significantly lower jitter than
DO Rev 0. DO Rev A terminals can achieve
instantaneous higher-rate transmission without
sacrificing transmit power efficiency with interference limited by the token bucket access control mechanism.
The adaptive token bucket mechanism allows
not only improved support for applications with
latency-sensitive data bursts, but also uniform
allocation independent of the burstiness of a
flow. While the use of rate transition probabilities in DO Rev 0 controls how quickly the access
terminal can transmit data from a given flow, the
use of the adaptive token bucket mechanism in
DO Rev A allows a quicker transition to a higher rate and also permits initial transmissions at a
higher data rate. Furthermore, the deterministic
token bucket mechanism reduces variation in
delay (jitter) compared to the probabilistic algorithm in DO Rev 0.
A source with a short data burst continues to
receive the same allocation over time and uses
the stored resources to transmit the data bursts.
This permits self-tuning for each flow. For example, a video flow generates short data bursts
periodically to convey scene changes. Since the
T2PInflow increases at a steady rate, it fills up
the token bucket, and this stored resource is
used to transmit the scene change information at
a high data rate, as needed, to achieve the
desired latency. This peak-to-average ratio is
controlled by the access network.
The adaptive token bucket mechanism also
specifies a saturation level for each flow, and a
bucket level in excess of the saturation level
indicates overallocation that may be due to
either a data limitation or a power amplifier
headroom limitation. In this event the T2PInflow reduces to the access network granted minimum value and starts increasing only when the
flow is no longer overallocated. The adaptive
token bucket mechanism also imposes a restriction on the T2PInflow increase based on the difference between the average T2PInflow and
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Page 83
T2POutflow. That is, the resource allocation to a
flow is a function of the resource utilization by
that flow. This enables self-tuning of the flow’s
resource allocation based on the arrival characteristics of the data source and the power amplifier headroom at the AT. Flows with a fixed
T2PInflow allocation (e.g., a low-rate delay-sensitive flow) stop T2PInflow increase once adequate T2PInflow has been accumulated for the
next burst of data.
Delay and throughput comparison between DO Rev. 0
and DO Rev. A with bursty source
103
Rate (kb/s)
BHUSHAN LAYOUT
DO Rev 0
DO Rev A
DO rev 0: avg. rate = 55.9 kb/s (16-slot avg.)
DO rev A: avg. rate = 53.5 kb/s (16-slot avg.)
102
101
100
Load-Sensitive Resource Allocation — The
uplink rate transition probabilities in DO Rev 0
are designed conservatively to ensure stable system performance when the uplink is heavily
loaded, leading to inefficient resource utilization
when the uplink is lightly loaded. DO Rev A
improves on the dynamics of resource utilization
by introducing load-sensitive resource allocation
that allows the ATs to use a greedy resource
allocation strategy subject to feedback control
from the access network. In other words, the
rate of increase in T2P allocation for a flow is
dependent on the system load level and allows a
trade-off between convergence rate and variation in resource allocation as a function of load.
If the DO Rev 0 transition probabilities were
designed assuming a lightly loaded sector, the
RoT CCDF tails would be excessive when the
sector is heavily loaded, resulting in loss of coverage and higher potential for instability. The
load-sensitive resource allocation in DO Rev A
IEEE Communications Magazine • February 2006
0
1000
2000
3000
4000
5000
6000
(a)
0.5
DO Rev 0: mean delay = 129.7 ms, max delay = 331.7 ms
DO Rev A: mean delay = 36.8 ms, max delay = 75.0 ms
Bit delay (s)
0.4
0.3
0.2
0.1
0
0
1000
2000
3000
Time (slot)
4000
5000
6000
(b)
n Figure 7. Throughput and delay comparison between 1xEV-DO Revision 0
and 1xEV-DO Revision A for a bursty data source.
103
Delay-sensitive, low-rate 1
Delay-sensitive, high-rate 1
Best effort 1
Delay-sensitive, low-rate 2
Delay-sensitive, high-rate 2
Best effort 2
102
Throughput (kb/s)
Multiflow Uplink MAC — The delay-sensitive
low-rate flow (e.g., VoIP) and delay-sensitive
high-rate flow (e.g., fixed-rate video telephony)
are assigned a fixed allocation that permits the
flow to use the desired system resources (up to a
certain T2PInflow) except under extreme system
loading. A fixed allocation attempts to provide a
circuit-like performance to the flow, while taking
advantage of statistical multiplexing when the
flow does not utilize its allocation. The delaysensitive elastic flow (e.g., adaptive-rate video
telephony) is assigned an elastic allocation with
a fixed component that permits this flow to utilize resources in addition to a fixed allocation if
the sector is lightly loaded. The delay-tolerant
best effort source (e.g., file transfer) utilizes the
resources not currently used by the higher-priority flows in the system.
We now illustrate the impact of power amplifier headroom limitations on flow throughput
and latency using the flows for which the priority
functions are as shown in Fig. 8. This effect is
illustrated in Fig. 8 for two ATs with the same
delay-sensitive low-rate, delay-sensitive highrate, and delay-tolerant best effort flows but with
different PA headroom limitations (due to ATs
in different locations experiencing different path
loss). We see that the delay-sensitive low-rate
flows achieve the desired allocation in both
cases, but the throughput achieved for the delaysensitive high-rate and best effort flows is different due to different PA headroom limits at the
two ATs. The relative priority of the flows at the
two ATs — higher priority for the delay-sensitive
high-rate flows relative to the best effort flows
— is maintained as the path loss experienced by
the terminals increases.
101
100
0
5
10
15
20
Increase in AT path loss (dB)
25
30
n Figure 8. Impact of PA headroom limitation on flow throughput at different
access terminals with the same flow priorities.
results in the desired behavior without increasing
the likelihood of system instability.
Explicit Capacity, Latency, and Fairness
Control — DO Rev A provides several mechanisms for explicit interference control:
• Maximum transmit T2P control as a function of serving sector pilot strength
• Short-term sector loading as a function of
downlink sector pilot strength, pilot
strength of other sectors in the AT’s active
set, and the corresponding DRCLock bit
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Page 84
with the rest of the bits made up of padding.
Improvement in packing efficiency for terminals
in poor channel conditions can be achieved by
the use of short packets with payload sizes of
128, 256, or 512 bits.
Biased MAC-case1
Default MAC
Biased MAC-case2
0.9
0.8
MEDIUM ACCESS CONTROL LAYER
0.7
Key enhancements to DO Rev A downlink MAC
layer are:
• Packet-division multiple access via the use
of multi-user packets
• One-to-many mapping of DRC index to
transmission formats
• Seamless adaptive server selection
• Application-adaptive physical layer PER
• Reduction in transmission delay via nullDRC to non-null rate mapping
cdf
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
AT relative throughput
n Figure 9. Reverse link rate shaping in 1xEV-DO Revision A.
• T2PInflow scaling as a function of downlink
serving sector pilot strength
Figure 9 shows examples of rate shaping for
the uplink, which is a form of explicit interference control. With appropriate choice of DO
Rev A uplink MAC channel parameters, any
desired normalized AT throughput and consequently interference distribution can be
achieved. For the examples shown in Fig. 9, the
fairness among users can be either decreased
(biased MAC case 1) or increased (biased MAC
case 2) as desired. DO Rev 0 MAC does not
provide mechanisms for uplink rate shaping.
DOWNLINK
PHYSICAL LAYER
Key enhancements to DO Rev A downlink physical layer are:
• Short packets (i.e., 128-, 256-, and 512-bit
packets)
• Higher peak data rates (3.1 Mb/s) and finer
rate quantization
DO Rev A downlink physical layer packets
are defined by their transmission formats. The
transmission format is an ordered triple defined
by the physical layer packet size (bits), nominal
packet duration (slots), and the preamble length
(chips). For instance, (128, 16, 1024) indicates
that the packet has a 128-bit payload, nominal
duration of 16 slots, and a 1024-chip preamble.
Transmission formats and their corresponding
code rate, modulation, and nominal data rates
are listed in [6]. DO Rev A introduces new packet sizes of 128, 256, 512, and 5120 bits in addition to the 1024-, 2048-, 3072-, and 4096-bit
packet sizes in DO Rev 0. In addition, DO Rev
A permits nominal spans of one through 16
slots, resulting in data rates ranging from 4.8
kb/s to 3.072 Mb/s.
The smallest physical layer packet size on DO
Rev 0 downlink is 1024 bits, and the packet may
contain only a few bits of delay-sensitive traffic
84
Packet-Division Multiple Access — Substantial improvement in link and packing efficiency
can be achieved by the use of multi-user packets
(MUPs), transmitting data to multiple ATs using
the same physical layer packet. This technique is
called packet-division multiple access (PDMA).
It enables DO Rev A to support a large number
of low-rate delay-sensitive applications. A MUP
is a single physical layer packet containing data
for multiple ATs (maximum of eight ATs per
packet). The downlink scheduler continues to
serve single-user packets (SUPs) using opportunistic scheduling to exploit multi-user diversity
where possible.
DRC Index to Transmission Format Mapping — A one-to-one mapping between requested DRC and data rates/packet sizes is used in
DO Rev 0. A more flexible mapping allows for
improved packing efficiency as well as better
matching of the requirements of the flow to the
physical layer transport. Each MAC packet may
be transmitted using several different transmission formats that are consistent with the MAC
packet size. As an example, the transmission formats (1024, 16, 1024), (1024, 8, 512), (1024, 4,
256), (1024, 2, 128), (1024, 1, 64), (1024, 2, 64),
and (1024, 4, 128) are consistent with a 994-bit
MAC packet. Each DRC index in DO Rev A
has a set of associated transmission formats for
single- user packet and multi-user packet. For
example, DRC index 0x3 is associated with transmission formats (128, 4, 256), (256, 4, 256), (512,
4, 256), and (1024, 4, 256), where (1024, 4, 256)
is defined as the canonical transmission format
and is the transmission format associated with
DRC index 0x3 in DO Rev 0. All the other consistent transmission formats above are called
non-canonical transmission formats. A detailed
listing of DRC indices and their associated transmission formats is provided in [6].
Since ATs always attempt to decode MUPs
with packet transmission formats of (128, 4,
256), (256, 4, 256), (512, 4, 256), and (1024, 4,
256), the access network can serve packets to an
AT whose DRC is erased using these transmission formats. This allows for improved performance of delay-sensitive applications.
Given a nominal PER target of 1 percent, use
of short packets (includes packets with payload
sizes less than 1024 bits and non-canonical SUPs)
and MUPs may result in a sub-1 percent physical
IEEE Communications Magazine • February 2006
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layer PER as the network may transmit packets
using a compatible transmission format that provides additional SINR margin. For example, a
terminal with a requested DRC corresponding
to the transmission format (5120, 1, 64) may be
served using a MUP with transmission format
(1024, 4, 1024).
Adaptive Server Selection — The DO Rev 0
downlink supports virtual soft handoff via adaptive server (base station) selection. Server
changes in DO Rev 0 may result in packet transmission delay that does not impact best effort
traffic, but may limit the performance of delaysensitive applications.
In DO Rev 0 ATs indicate downlink server
changes via the DRC channel by changing the
serving sector information (also called the DRC
cover). When the access network detects a consistent change in the DRC cover, it reroutes the
data queue for the AT to the new server. During
this transition phase, neither the old nor the new
server is capable of transmitting packets to the
AT. DO Rev A eliminates this transmission
delay via the use of the data source control
(DSC) channel. Each AT uses the DSC channel
to provide the access network early indication of
the exact instant of time at which the change in
downlink server takes place, as shown in Fig. 10.
As a result, the data queue is already set up at
the new server by the time the AT points its
DRC to the new server.
Application-Adaptive Physical Layer PER —
DO Rev A systems permit access network control of the downlink physical layer PER based on
the composition of the flows to an AT. This is
accomplished by providing the AT with a mapping from the tentative DRC to a transmitted
DRC. With an appropriate mapping, additional
rounds of H-ARQ are added to the physical
layer without affecting the overall downlink
capacity. For example, a mapping from a tentative DRC corresponding to the transmission format of (4096, 1, 64) to a transmitted DRC
corresponding to the transmission format of
(4096, 2, 64) results in an additional slot being
transmitted for this packet 1 percent of the time
(assuming a target PER of 1 percent after one
slot) and permits achieving approximately 0.01
percent PER after two slots.
Null-Rate Conversion — The DO Rev A
downlink supports null-rate conversion where
the null-rate DRC received from the AT can be
mapped to transmission formats (1024, 16, 1024),
(512, 16, 1024), and (256, 16, 1024). Since ATs
that support MUP reception attempt to detect
the above transmission formats, null-rate conversion provides the access network a mechanism to
serve ATs with null-rate requested DRC.
In a vast majority of cases, a null-rate DRC
converted to the transmission format (1024, 16,
1024) results in an effective data rate exceeding
38.4 kb/s. Similar gains are seen for smaller payload sizes transmitted in response to a null-rate
DRC. In addition, the use of short packets and
non-canonical SUPs for low-rate delay-sensitive
traffic improves downlink transmit efficiency
(transmission of 100 bits of data using transmis-
IEEE Communications Magazine • February 2006
Transmit delay
Forward link serving
cell BS1
t1
DRC cover
change
DRC cover
change
detection
at BS1 and
BS2
t2
Time
Qtransfer
to BS2
IS-856 Revision 0
Forward link serving cell BS1
Forward link serving
cell BS2
t1
DSC cover
change
DRC cover
change
detection
at BS1 and
BS2
Forward link serving
cell BS2
t2
Qtransfer
to BS2
DRC
cover
change
Time
IS-856 Revision A
n Figure 10. Adaptive server selection (DO Rev 0 vs. DO Rev A).
sion format (128, 4, 1024) results in a worst-case
usage of four slots on the downlink).
PERFORMANCE
SIMULATION MODELS AND PARAMETERS
The capacity simulations are based on a network
of 57 sectors arranged in a hexagonal grid as
specified in [5]. The channel models, A through
E, are also specified in [5]. The system simulation is complete in the sense that all algorithms
at each layer within the access network and ATs
are modeled. More specifically, the simulations
include a model for the downlink equalizer
along with the thermal noise set by the receiver
noise figure, post-AGC receiver self noise, baseband pulse shape, and the effect of base station
waveform quality (rho factor). In addition, the
signaling on both the downlink channels (ARQ
and RPC) and uplink channels (DRC, DSC,
RRI, and ACK) is modeled. The uplink outer
loop power control and MAC algorithm with
direct RoT measurement are also modeled. The
downlink scheduler with support for MUPs and
short packets is simulated along with the MAC
channel power allocation algorithm.
SYSTEM PERFORMANCE
Table 1 summarizes the results using the fullbuffer model for both DO Rev 0 and DO Rev A
systems. The forward link capacity numbers for
DO Rev A assume the use of an MMSE equalizer.
Table 2 shows the comparison of uplink
capacity and latency between DO Rev 0 and DO
Rev A. The sector capacity for DO Rev A with
10 ATs per sector, all with 8-slot termination
target, is roughly the same as that for DO Rev 0,
but with over 50 percent reduction in mean
delay (including queuing and transmission
delay). On the other hand, when using a 16-slot
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Criteria
Forward link sector capacity
(full buffer)
Reverse link sector capacity
(full buffer)
1xEV-DO Rev 0
1xEV-DO Rev A
16 users/sector dual
antenna receiver
1200 kb/s
1500 kb/s
16 users/sector dual
antenna receiver
310 kb/s
500 kb/s
16 users/sector fourantenna receiver
600 kb/s
1200 kb/s
n Table 1. DO Rev A and DO Rev 0 performance comparisons.
DO Rev 0
Number
antenna
Number
of ATs
Sector
capacity (kb/s)
Mean RoT
(dB)
Mean delay (ms)
2
10
320
5
40
DO Rev A 8-slot termination target
ACKNOWLEDGMENTS
Number
antenna
Number
of ATs
Sector
capacity (kb/s)
Mean RoT
(dB)
Mean delay (ms)
2
10
318
5.2
15.2
DO Rev A 16-slot termination target
The authors thank Matt Grob and Rajesh Pankaj
for their constructive comments that led to many
improvements to this article, and Mehmet Gurelli for simulation data used for several illustrations and the applications capacity.
REFERENCES
Number
antenna
Number
of ATs
Sector
capacity (kb/s)
Mean RoT
(dB)
Mean delay (ms)
2
10
628
5.2
39.5
4
10
1325
5.6
40
n Table 2. DO Rev 0 and DO Rev A (capacity and latency trade-off).
termination target, the sector capacity for DO
Rev A is almost doubled relative to that of DO
Rev 0 while achieving roughly the same mean
delay.
A 32-byte ping transmission over an experimental 1xEV-DO Revision A system showed
that 90 percent of the pings experience an endto-end delay of less than 30 ms. and nearly all
packets experience an end-to-end delay of less
than 32 ms.
SUMMARY AND CONCLUSIONS
1xEV-DO Revision A is designed to offer efficient support for both delay-sensitive and delaytolerant applications. Salient features added to
1xEV-DO Revision A are short packets and
multi-user packets on the downlink, and physical
layer ARQ and multiflow reverse link MAC
layer on the uplink. The inclusion of these features provides substantial improvement in the
performance of delay-sensitive applications such
as VoIP, gaming, and video telephony.
1xEV-DO Revision A is fully backward compatible with 1xEV-DO Revision 0 networks, and
an upgrade involves only a change to the mobile
station and base station ASICs with no other
change to the base station hardware. 1xEV-DO
Revision A systems deliver high spectral efficien-
86
cy, support large numbers of mobile users, sub30 ms round-trip latencies to support interactive
applications, provide performance comparable to
toll-quality voice applications, support end-toend IP QoS that allows operators to maximize
revenue through tiered services, and provide
comprehensive network control over terminal
behavior.
[1] P. Bender et al., “CDMA/HDR: A Bandwidth Efficient
High-Speed Data Service for Nomadic Users,” IEEE Commun. Mag., vol. 38, July 2000, pp. 70–77.
[2] P. J. Black and M. I. Gurelli, “Capacity Simulation of
CDMA2000 1xEV Wireless Internet Access System,” 3rd
IEEE Int’l. Conf. Mobile and Wireless Commun. Networks, Recife, Brazil, Aug. 2001.
[3] Y. Jou, “Developments in Third Generation (3G) CDMA
Technology,” Proc. IEEE 6th Symp. Spread-Spectrum
Tech. and App., Newark, NJ, Sept. 2000.
[4] Q. Wu and E. Esteves, Advances in 3G Enhanced Technologies for Wireless Communications J. Wang and T.
Ng, Eds., Ch. 4, 2002.
[5] 3GPP2 TSG-C WG3 Contribution C30-20031002-004,
“1xEV-DO Evaluation Methodology,” Oct. 2004.
[6] 3GPP2 C.S20024-A v1.0, “CDMA2000 High Rate Packet
Data Air Interface Specification,” Mar. 2004.
ADDITIONAL READING
[1] 3GPP2 C.S20024 v2.0, “CDMA2000 High Rate Packet
Data Air Interface Specification,” Oct. 2000.
[2] E. Esteves, P. J. Black, and M. I. Gurelli. “Link Adaptation
Techniques for High-Speed Packet Data in Third Generation
Cellular Systems,” Euro. Wireless Conf., 2002.
[3] N. Bhushan and P. J. Black, “Forward Link Coding and
Modulation Design for CDMA2000 1xEV (IS-856),”
PIMRC 2002, Lisbon, Portugal, Sept. 2002.
[4] S. Chakravarty, R. Pankaj, and E. Esteves, “An Algorithm
for Reverse Traffic Channel Rate Control for CDMA2000
High Rate Packet Data Systems,” GLOBECOM 2001, San
Antonio, TX, Nov. 2001.
[5] 3GPP2 TSG-C WG3 Contribution C30-20031013-209R4,
“Link Budget for 1xEV-DO Revision A,” Oct. 2004.
[6] M. Fan et al., “On the Reverse Link Performance of
CDMA2000 1xEV-DO Revision A System,” ICC 2005.
[7] C. Lott et al., “Reverse Traffic Channel MAC Design of
CDMA2000 1xEV-DO Revision A System,” VTC 2005.
BIOGRAPHIES
N AGA B HUSHAN (nbhush@qualcomm.com) obtained his
B.Tech. degree in electronics from the Indian Institute of
Technology, Chennai, in 1989. He pursued his graduate
study at Cornell University, where he secured his M.S. and
Ph.D. degrees in 1992 and 1994, respectively, both in electrical engineering. He has been working as a systems engi-
IEEE Communications Magazine • February 2006
BHUSHAN LAYOUT
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Page 87
neer at QUALCOMM since 1994, where he is now vice president of technology in the Corporate R&D group. During the
course of his graduate study and professional career at
QUALCOMM, he has been involved in the analysis, design,
and development of high-speed wireless communication
systems, with emphasis on channel coding, link adaptation
techniques, modem design, advanced transmission and
receiver techniques, MAC design, and performance optimization for high-speed wireless packet data systems.
CHRISTOPHER LOTT received his B.S.E.E. from Massachusetts
Institute of Technology (MIT), his M.S.E.E. from Stanford,
and his Ph.D. from the University of Michigan, where he
received the Lucent Distinguished Dissertation award. Prior
to joining QUALCOMM he worked at Hewlett-Packard on
applied statistical signal processing projects, at Trimble
Navigation on GPS and Inmarsat Std-C system development, and as a technical consultant in Trimble's Asian market. Since he joined QUALCOMM in 2001 he has been
working on 1xEV-DO system design and standardization,
with an emphasis on resource allocation problems, QoS,
and MAC design. His research interests include stochastic
systems, resource allocation, distributed algorithms, communication theory, dynamical systems, and wireless networks.
PETER J. BLACK is senior vice president of technology for Corporate Research and Development, QUALCOMM Incorporated. He joined QUALCOMM in April 1993, where he was
first engaged in the system design and development of
dual mode CDMA/AMPS mobile station ASICs. In 1997 he
co-led the system design and prototype development of a
high-speed cellular packet data system known as HDR. This
system design was the framework for the cdma2000 highrate packet data standard more commonly known as 1xEVDO, published in 2000. He also co-led the subsequent
commercialization of 1xEVDO, which has now achieved
large-scale deployments in all major markets. Since 2001
he has continued to contribute to the evolution and
enhancements of the EVDO standard and products. Most
recent initiatives include hybrid OFDM broadcast, VOIP,
and multicarrier EVDO. He received his B.E. degree in electrical engineering from the University of Queensland, Australia, in 1985. He received his M.S.E.E. and Ph.D. degrees
from Stanford University, California, in 1990 and 1993,
respectively. He is a Fulbright Scholar and was awarded the
University Medal by the University of Queensland in 1985.
R ASHID A TTAR (rattar@qualcomm.com) obtained his B.E.
degree in electronics from Bombay University in 1994 and
M.S.E.E from Syracuse University in 1996. He joined QUALCOMM in June 1996, where he was first engaged in the
integration of IS-95-based cellular systems. Since 1998 he
has been working in the Corporate Research and Development group on 1xEV-DO system design, development,
standardization, and optimization as a senior staff engineer/manager. He is currently working on 1xEV-DO Revision
B and future technologies, and pursuing his Ph.D. at the
University of California at San Diego, under the guidance
of Prof. Larry Milstein. His research interests include topics
in multi-access techniques and multihop cellular networks.
IEEE Communications Magazine • February 2006
Additionally, he has been awarded several patents throughout his career.
Y U -C HEUN J OU received his B.S.E.E. degree from National
Taiwan University, and his M.S.E.E. and Ph.D. degrees from
the University of Southern California. He has been with
QUALCOMM since 1989 and is currently vice president of
technology. He served as chief technology officer of QUALCOMM China from November 2003 to June 2005. At
QUALCOMM he has been involved in designing, developing, testing, and standardizing CDMA cellular technologies.
He was also involved in the design of the Globalstar LEO
satellite system. He is a key contributor to the design and
standardization of the third-generation (3G) wireless system for voice and data services, especially to the development of the IS-2000 (cdma2000 1X) and IS-856 (cdma2000
1X-EV-DO) series of standards. He has a wide area of interests in wireless communications, recently focusing on
designing wireless data communication systems to support
applications with different QoS requirements as well as
designing advanced receivers to maximize the performance
of existing standards. He is the author or co-author of
approximately 50 U.S. patents.
M INGXI F AN received his Bachelor’s, Master’s, and Ph.D
degrees in electrical engineering in 1999 and 2002, respectively, from MIT. From 1996 to 2001 he was a research
intern with the systems group at Hughes Network Systems,
San Diego, California, where he designed and implemented
various signal processing algorithms for several wireless
and satellite communication systems. In summer 2000 he
was a DSP consultant and project leader at Vanu, Inc.,
Cambridge, Massachusetts, where he implemented the
physical layer processing of an IS-95B system on a software
radio platform. He joined QUALCOMM, Inc. in July 2002
and is currently working on cdma20001xEV-DO related
research, implementation, and standards development. His
research interests include topics in spread-spectrum modulation, multiuser detection, and adaptive antenna array. He
received the Ernst A. Guillemin EE Master's thesis award
from MIT in June 1999.
1xEV-DO Revision A
is designed to offer
efficient support for
both delay-sensitive
and delay-tolerant
applications. Salient
features added to
1xEV-DO Revision A
are short-packets
and multi-user
packets on the
downlink, and
physical layer ARQ
and multi-flow
reverse link MAC
layer on the uplink.
DONNA GHOSH received a Ph.D. degree in computer science
and engineering from the Pennsylvania State University,
University Park, in June 2003. Her Ph.D. research work was
awarded the NSF-ITR grant in 2002 in the area of highspeed networking. She joined the Corporate Research and
Development Group at QUALCOMM Incorporated, San
Diego in July 2003. Her research interests are in the areas
of pricing and QoS for wired and wireless networks, and
stochastic modeling and analysis for wired and wireless
networks.
JEAN AU received his B.A. (economic), B.Sc and M.Sc (both
in electrical engineering) from Queen's University, Kingston,
Canada in 1995, 1996, and 1999 respectively. He joined
QUALCOMM in 1999 as a systems engineer with the Corporate Research and Development Department. He was
involved in the design, verification, optimization, and
deployment of the CDMA2000 1xEV-DO system. Several
patents have been filed by him throughout his career.
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