IEEE C802.16m-08_417
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
UL fast bandwidth request control schemes
Date
Submitted
2008-05-05
Source(s)
Jimin Liu, Wu Zheng, Xiaobing Leng,
Gang Shen, Kaibin Zhang, Shan Jin
Voice: + 86-21-50554550-3712
Fax: + 86-21-50554554
Email: Jimin.Liu@alcatel-sbell.com.cn
Gang.A.Shen@alcatel-sbell.com.cn
Kaibin.Zhang@alcatel-sbell.com.cn
Alcatel Shanghai Bell
*<http://standards.ieee.org/faqs/affiliationFAQ.html>
Re:
Call for Contributions for 802.16m-08_016r1 on uplink control structures
This contribution pertains to the uplink control structures
Abstract
This contribution proposes an uplink bandwidth request scheme for latency-sensitive services in
code-division-multiplexing UL control channel
Purpose
For IEEE 802.16m discussion and eventual adoption
Notice
Release
Patent
Policy
This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It
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UL Fast Bandwidth Request Control Scheme
Jimin Liu, Wu Zheng, Xiaobing Leng, Gang Shen, Kaibin Zhang, Shan Jin
Alcatel Shanghai Bell
Introduction
New types of services, such as interactive gaming, interactive streaming media, are emerging to be supported in
802.16m systems. There are several characteristics for interactive traffic. For example, short-packet messages
are sent at irregular intervals, as shown in Fig.1, and they must be delivered with the minimum delay. In legacy
Bandwidth request
Traffic bulk
1
Time
IEEE C802.16m-08_417
802.16e system, the uplink bandwidth can be requested by one of the bandwidth request schemes, such as
piggyback, polling, and contention-based bandwidth request [1]. Due to the unexpected occurrence of traffic
bursts, contention-based bandwidth request method is generally preferred.
Figure 1: Illustration of Interactive Traffic
Fig.2 shows the legacy contention-based bandwidth request procedure in legacy 16e system. Before data can be
transported by the MS, there are at least three rounds of negotiation between the BS and the MS. For the entire
system, it is inefficient to transport short packets with such high overhead and long delay. For rtPS and ert-PS
services, the delay due to such three rounds of signaling interaction needs to be reduced and the bandwidth
request efficiency should be improved. An uplink fast bandwidth request/allocation scheme is proposed using a
CDM (code-division-multiplexing) method in this contribution.
BS
MS
UL-MAP with BR request region
BR-Req CDMA code
UL-MAP with CDMA Alloc IE
BR-Req header
UL-MAP with allocation
data
Figure 2: Contention-based BR request procedure in legacy 16e systems
Proposed UL fast bandwidth request control scheme
The objective of the proposed fast bandwidth request scheme is to reduce the signaling interaction between the
MS and the BS. It is accomplished in the first signaling transmission from MS to BS by taking the information
of requested bandwidth and requested CID. The accelerated bandwidth request procedure is illustrated in Fig. 3
below:
BS
MS
UL-MAP with Fast BR request region
CDM (BR-Req)
UL-MAP with allocation
data
Figure 3: Proposed contention-based BR request procedure
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IEEE C802.16m-08_417
1. BS broadcasts UL-MAP with a Fast BR request region to MS. This region is another resource block in UL
subframe which is different from what the legacy BR-Req allocates. The region can be divided into multiple
Fast BR-slots.
2. MS transmits Fast BR-Req messages in the BR-slot dedicatedly specified by the BS in a spreading way. The
objective of re-designing the Fast BR-Req message format, instead of legacy BR-Req message format, is to
reduce delivering information bits as much as possible without compromising the overall performance. A
Fast BR-Req message may consist of the connection information, requested bandwidth and CRC bits. As
soon as MS sends the BR-Req, a timer starts for retransmission if no response from BS is available.
3. Once BS successfully detects the Fast bandwidth request signal from the MSs, it then performs scheduling
to allocate resource blocks for data packet delivery for the MS. Then MS transmits its data stored in its
queue within the assigned time/frequency resource block.
Code-Division Multiplexing and Mapping
Channelization code specified by BS
(Walsh code)
Pilot
BR-Req 1
+
Mapping to
BR Slot
Channelization code 1
Scrambling code
BR-Req 2
Channelization code 2 specified by
BS (Walsh code)
Figure 4: CDM and mapping of two Fast BR-Reqs at one MS
Fig. 4 shows a code-division multiplexing framework, in which two BR-Reqs are multiplexed and mapped into
one Fast BR slot. The pilot sequence is used for channel estimation in the Fast BR slot at the BS to decode the
BR-Req correctly. The scrambling code is specified by BS for user differentiation. It can be assigned and
informed by BS when MS perform network entry or MS establish a real time connection. After scrambling, each
bit of generated sequences is mapped into a two-dimensional BR-slot as illustrated in Fig. 5. The portion of the
specified scrambling code is used to be the preamble which is inserted before the generated CDM sequences.
The objective of the preamble is to detect whether the bandwidth request is available before further decoding the
new BR-Request. The left-upper subcarrier carries the first bit of the generated sequences. The following bits
are mapped in subcarrier-first directions, so the (M-1)th subcarrier is mapped to the (M-1)th subcarrier. Then the
filling of the second line in the BR slot started from the first subcarrier to the (M-1)th subcarrier. It continues to
proceed until all subcarriers in all symbols are filled up.
Subcarrier
N-1
M-1
Symbol
Figure 5: Mapping of a CDM sequence in a BR-slot
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IEEE C802.16m-08_417
Owing to the spread gain of channelization code, one BR slot can accommodates a limited number of
concurrent users with bandwidth requests. It is expected that MS can be flexibly assigned to one of the BR-slots.
The tradeoff between the number of BR slot and utilization efficiency can be obtained through careful
adjustments.
Proposed Text for SDD
Insert the following text into SDD Section 11 – Physical Layer [2]
------------------------------- Text Start
---------------------------------------------------
11.x: UL Control Structure
11.x.x Fast bandwidth request control channel
16m BS should allocate a UL contention-based control channel for fast bandwidth request/allocation. An MS
sends a Fast BR-Req message in the control channel, which includes the information of the connection for
which UL bandwidth is requested, and the number of bytes requested. The Fast BR-Req messages from multiple
MSs are code-division-multiplexing.
References
[1] IEEE P80216Rev2_D4, “Part 16: Air Interface for Broadband Wireless Access Systems”
[2] IEEE 802.16m-08/003r1, “The Draft IEEE 802.16m System Description Document”
4