Proceedings of 2010 IEEE International Conference on Ultra-Wideband (ICUWB2010)
Abhishek Bit, Dr. Martin Orehek, Waqar Zia
Student:
Adviser:
ID:M9920108
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Abstract
INTRODUCTION
COMPARATIVE ANALYSIS
A. Basic Architecture
B. Radio Technologies Used
C. Broadcast Support
D. Number of Devices Supported by a Host
E. Extension of the Basic Cell
F. Throughputs
G. Device Association Mechanisms
H. Bluetooth Profiles
I. Power Consumption
J. Technology Maturity and Market Penetration
K. Cost
CONCLUSION & SUMMARY
REFERENCES
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This paper presents the results of the comparative
analysis of two different protocols that use or could
potentially use the Ultra Wideband (UWB) radio
technology – Certified Wireless-USB and Bluetooth 3.0
with UWB.
Bluetooth 3.0 with UWB is found to have a number of
advantages over Certified Wireless-USB. These
include lesser overheads, higher throughputs, higher
power efficiency, better device association
mechanisms, dedicated profiles, and support for data
broadcast.
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The W-USB Specification Revision 1.0 was developed
by the USB Implementers Forum (USB-IF). The
protocol utilizes the common WiMedia MB-OFDM
UWB radio platform for its high data-rate operation.
Certified Wireless-USB (CW-USB) is basically that
flavour of W-USB that is promoted and standardized
by the USB-IF.
The protocol can be classified as a full-blown MAC in
its own right.
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Bluetooth is a wireless communication standard
intended for exchanging data over short-distances
between fixed as well as mobile devices.
Bluetooth Core Specification Version 3.0 + High
Speed (HS), or Bluetooth 3.0 is the latest iteration of
the short-range wireless technology from Bluetooth
Special Interest Group (SIG).
Instead of UWB, 802.11g was preferred as the
alternate high speed radio.
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However, the Bluetooth 3.0 architecture consists of a
‘generic’ Alternate MAC/PHY (AMP) layer, and the
idea of incorporating the UWB radio, as the high
speed alternative to 802.11g, is still not completely
out of the question.
The term ‘generic’ underlines the fact that Bluetooth
3.0 has been architected to use any approved MAC
and PHY (including WiMedia UWB MAC and PHY) for
its high data rate operation.
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Furthermore, since Bluetooth 3.0 achieves its 24
Mb/s transfer speeds by pairing devices and then
initiating a Wi-Fi connection between them, it could
do the same with UWB technology, if it was built in.
UWB technology continues to be a potential high
speed alternative for the next generation of Bluetooth.
Significantly higher data rates, energy efficiency,
better tolerance to interference, are some key
advantages of UWB over 802.11g.
Throughout the discussion in this work, the Bluetooth
3.0 protocol is assumed to use UWB as the high
speed radio technology.
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A. Basic Architecture
The CW-USB architecture is based on the hub-spoke
model where one device (the Host) is the master and
the other devices are the slaves.
In such a star formation, it is the Host that controls
the entire network of other devices.
Different softwares are used for a CW-USB Host and a
CW-USB Device i.e. the end-to-end connection
architecture is not symmetric.
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A CW-USB product can either be a limited CW-USB
Host, a CW-USB Device or a device capable of
assuming both roles (Dual Role Device – DRD).
The master-slave topology of CWUSB has another
major drawback in a network environment, where one
slave can talk to another slave only through the
master.
This also increases the power consumption of the
Hosts as they have to control all slaves.
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In Bluetooth 3.0, though in any given piconet, one
device assumes the role of the master, all devices are
born equal.
The Bluetooth 3.0 implementation is symmetric. This
implies that any device that supports Bluetooth 3.0
can assume the role of either a master or a slave.
The Bluetooth 3.0 software on both sides is the same.
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Bluetooth 3.0 uses two radio technologies – the
Bluetooth BR/EDR radio and the high speed UWB
radio.
This allows switching to UWB in case of high speed
communications and reverting back to Bluetooth
BR/EDR when the high speed radio link is no longer
needed.
Protocol complexity is thus increased through an
additional AMP manager that controls switching and
manages the radios.
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CW-USB, on the other hand, uses the UWB radio only.
This translates to lower protocol complexity
compared to Bluetooth 3.0. Connection establishment
in Bluetooth takes place out-ofband with respect to
the high speed UWB radio.
This is in contrast to CW-USB, which uses a Device
Notification Time Slot (DNTS) mechanism and all
communication takes place over UWB. Connection
setup time is thus expected to be higher with
Bluetooth 3.0.
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There is no mechanism that supports data broadcast in
WiMedia MAC. The Micro-scheduled Management Control
Proceedings of 2010 IEEE International Conference on
Ultra-Wideband (ICUWB2010) (MMC) frames in CW-USB are
“control frames” that are effectively broadcast.
The specification does not allow broadcast for user data.
In Bluetooth 3.0 however, the connectionless L2CAP
channels allow broadcast transmissions between the
master and the slaves in a piconet, over the BR/EDR radio.
Thus, a Bluetooth 3.0 implementation with UWB will have
data broadcast capability, but over the low bit rate radio.
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In Bluetooth, there can be at most 7 devices (active slaves)
connected to the host in a piconet.
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The protocol also supports as many as 255 parked devices
(inactive slaves) in the same piconet.
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WiMedia UWB MAC allows support for a maximum of 48
devices through 48 distinct Beacons.
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However, in Bluetooth 3.0, the BR/EDR link is left in the
active state, while the AMP UWB link is used for the high
speed communication between the same master-slave pair.
Thus, theoretically, the Bluetooth 3.0 with UWB can
support 7 active connections and 255 inactive connections.
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The number of active connections however, can possibly
be increased by putting the Bluetooth BR/EDR connection
into the parked state while high speed transfer takes place
over the UWB radio.
CW-USB on the other hand, can support 48 devices (active
connections) with a single host.
Bluetooth 3.0 has a slight disadvantage when it comes to
the maximum number of active connections supported by
a single host.
However, at any given time there can be a maximum of
262 (255+7) devices (inactive slaves included) in a single
piconet.
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As discussed earlier, Bluetooth 3.0 employs a
symmetric end-to-end architecture. Every Bluetooth
3.0 device is capable of assuming the role of either a
master or that a slave.
Therefore, in Bluetooth, the basic piconet architecture
can be easily extended to form a scatternet, with one
of the Bluetooth devices assuming the role of a
master in one piconet and that of a slave in the other,
or functioning as a slave in more than one piconet.
The number of active devices attached to a host
within one piconet remains the same (maximum of 7).
A Bluetooth device can serve as a master in one
piconet only.
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A CW-USB Device cannot assume both roles (unless
the complete CW-USB Host functionality is
incorporated within the Device as well). CW-USB puts
a clear demarcation between a Host and a Device.
The only way in which the star network can be
expanded is when one CW-USB Device acts as a slave
for more than one Host. Thus, the extension of a
basic cell in case of CW-USB is an extended star
network.
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Bluetooth 3.0 offers an advantage over CW-USB in
terms of achievable data throughputs.
This is owing to the following reasons:
• Higher signalling overhead in CW-USB owing to MMC frames. Control
information in CW-USB is explicitly exchanged through MMC frames (this is
in addition to Beacon slots used for signalling such as DRP reservations).
• Maximum allowable data payload size in case of Bluetooth 3.0 (with UWB) is
4071 bytes (4075 bytes – 4 bytes for L2CAP header), and for CW-USB it is
3582 bytes (3584 bytes – 2 bytes for WUSB header).
This again results in slightly higher data throughput
in case of Bluetooth 3.0.
This frame size difference is significant when large
data transfers are taken into account. With a
maximum allowable burst size of 16 packets, this
payload difference translates to a (4071 – 3582) bytes
x16 = 7824 bytes difference
• CW-USB uses dedicated time slots called Device
Notification Time Slots (DNTS) for several
notifications such as initial connection establishment
and communication resumption after flow control.
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The duration and number of such slots depends on
host implementation. CW-USB solutions from CSR use
a DNTS slot period of 24 μs with 8 DNTS slots.
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Bluetooth has its own way of releasing time when it is
flow controlling.
This is done through special frames called TC or ZA
frames. Moreover, connection establishment in
Bluetooth takes place over Bluetooth BR/EDR radios.
Therefore, in Bluetooth 3.0 with UWB implementation,
there is no need for the DNTS mechanism. The DNTS
slots thus are a clear overhead in case of CW-USB.
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With the abovementioned constraints in mind,
maximum throughput estimates for both protocols
were plotted using Matlab. The following
assumptions were made:
• Maximum burst size of 16 data packets for both protocols.
• Data payload transmission at the rate of 480 Mb/s (Fig. 1) and 53.3 Mb/s
(Fig. 2).
• Short burst preambles for all but first data packet.
• 8 DNTS slots of 24 μs each in CW-USB burst transaction group.
• An MMC frame ahead of the data burst in CW-USB.
• MIFS of 1.875 μs between burst data packets.
• SIFS of 10 μs between control frames and data packets.
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The throughputs were calculated as the ratio of the user data to
the total data transmitted (including protocol overheads and
taking into account the abovementioned assumptions).
The results in Fig. 1 indicate that theoretically, Bluetooth 3.0
with UWB would give a better throughput performance than
CWUSB.
With Bluetooth 3.0, theoretical maximum throughputs of 386
Mb/s (with data rates of 480 Mb/s) could be achieved. In case of
CW-USB, the maximum attainable throughput is lower at 328
Mb/s (with data rates of 480 Mb/s).
At the lowest data rate (53.3 Mb/s); the difference between the
throughputs for the two protocols is low, though still in favour of
Bluetooth 3.0 with UWB implementation (Fig. 2).
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Graphs were also plotted to compare maximum
attainable throughputs for the two protocols for nonbursty data traffic with the acknowledgment policy
set to No-ACK.
The following changes were made from the previous
assumptions:
• Normal PLCP preamble time of 9.375 μs.
• SIFS of 10 μs between all data frames (no MIFS).
• No acknowledgement frames (No-ACK policy).
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The plots (shown in Fig. 3) indicate drops in
maximum attainable throughputs for both protocols
when compared to the burst data traffic scenario.
The throughputs for Bluetooth 3.0 however, are still
higher than that of CW-USB.
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The WiMedia PHY supports data rates of 53.3, 80,
106.7, 160, 200, 320, 400 and 480 Mb/s. When data
reliability is critical, lower bit-rates are used.
The maximum data throughputs that can be achieved
with each of these data rates for Bluetooth 3.0 and
Certified Wireless-USB were computed using Matlab.
They are plotted in Fig. 4 for burst data traffic.
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The difference between the attainable throughputs for the two
protocols increases as the data rates are increased.
The difference is minimum (1.1916 Mb/s) for a bit-rate of 53.3
Mb/s and maximum (57.3 Mb/s) for 480 Mb/s data rate. This is
because at low data rates, more time is needed for user data
transmission.
Hence, the overhead ratio (computed as the ratio of the
transmission time for signalling overhead to the total
transmission time for the complete data transaction) is reduced.
From a data communication point of view, even a difference of
1.1916 Mb/s is significant. Note that the highest data rate (one
way) supported by Bluetooth BR radio is only 721 Kb/s.
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Bluetooth 3.0, in contrast to CW-USB, supports a number of
device association mechanisms. It uses Secure Simple Pairing
(SSP) to simplify the device pairing procedure, and maintain or
improve security (protection against passive eavesdropping and
MITM attacks).
As many as four association models are defined under SSP –
Numeric Comparison, Just Works, Out of Band or NFC, and
Passkey Entry.
One of the device association mechanisms in CW-USB employs
the use of a physical USB cable to establish a first time secure
connection in effect violating the whole essence of wireless
communication.
Clearly, Bluetooth has an advantage over CW-USB when it comes
to support for device association models.
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The Bluetooth protocol stack includes dedicated profiles
which define the behaviour through which Bluetooth
enabled devices “talk” to each other.
As many as 22 profiles are supported. Each of these
profiles generally includes a user interface, information
about dependencies on other profiles and parts of the
Bluetooth stack to be used.
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The specification also allows developers to create their
own applications to work with other Bluetooth devices.
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CW-USB specification does not include any such profiles.
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In Bluetooth 3.0 device discovery, connection
establishment and maintenance, and profile
configuration use the Bluetooth (BR/EDR) radio,
while bulky data transfer uses the faster alternate
MAC and PHY (UWB).
In this way, when the system is idle, the proven
low power configuration models of Bluetooth are
used, and only in case of a large data transfer,
the system switches to the UWB radio.
When the high speed is not required, the link is
turned off or put in idle mode.
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CW-USB, on the other hand, utilizes the UWB for all
radio communication – including discovery,
connection setup and radio link management.
This leads to higher power consumption (continuous
data processing at say 300 Mb/s for UWB radio) in
CW-USB as compared to Bluetooth 3.0 where one has
the option to utilize the lower bit-rate radios.
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CW-USB is a published standard. This is probably its main
advantage. W-USB solutions in the form of wireless display
adapters, wireless docking stations are available in the market.
The technology however, has not yet penetrated the mobile
device market.
Bluetooth 3.0 on the other hand, was released in April in 2009.
With Bluetooth and Wi-Fi already present in smart phones and
other handheld devices, the newer high speed version should
only be a software upgrade over the existing BR/EDR version.
However, the use of UWB instead of Wi-Fi (802.11g), as the
underlying high speed radio, is an improvement to the standard
suggested as one of the outcomes of this study.
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An end-to-end Bluetooth 3.0 solution would cost
more than that of CW-USB mainly due to the
following reasons:
• There would be two radio controllers in Bluetooth 3.0 (the Bluetooth
and the AMP-UWB controller) against the single UWB baseband
controller in CW-USB.
• The symmetric Bluetooth 3.0 architecture would imply that the
complete software stack is used on both sides. CW-USB makes a
distinction between a Host and a Device, with the Host managing
bulk of the data communication.
So, in case of many Devices connected to the Host,
the CW-USB solution would have the cost benefit over
Bluetooth 3.0.
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The results of the comparative study for Bluetooth
3.0 with UWB and CW-USB can be summarized using
the following table (Table I).
The Bluetooth 3.0 protocol has a number of
advantages which include a symmetric end-to-end
architecture, higher throughputs, power efficiency,
support for user-data broadcast, association models,
support for dedicated profiles, and scope for better
mobile market penetration.
The Bluetooth 3.0 protocol with UWB as the alternate
high speed radio technology, is therefore preferred
over CW-USB, and recommended for integration into
mobile devices.
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[1] E. Ferro, and F. Potorti, “Bluetooth and Wi-Fi protocols:
A survey and a comparison,” IEEE Wireless
Communications Magazine, June 30, 2004.
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[2] D. A. Gratton, “Ultra Wideband: I’ll be back,” Incisor,
Issue 135, pp. 13- 14, June 2009.
[3] Wireless-USB Specification, USB-IF, Revision 1.0, May
12, 2005.
[4] Bluetooth 3.0 + HS Specification, Bluetooth SIG, Vol. 0,
April 21, 2009.
[5] ECMA-368, “High Rate Ultra Wideband PHY and MAC
Standard,” 3rd edition, December 2008.
[6] J. Walker, “Why Mix Bluetooth with Wi-Fi?”, Wireless
Alert section in Network World, May 4, 2009.
[7] G. Heidari, WiMedia UWB – Technology of Choice for
Wireless-USB and Bluetooth, John Wiley & Sons Ltd., 2008
edition.