1. Overhead Reduction for the Identification of Anonymous Ranging Response
Document Number: IEEE C802.16m-09/0147
Date Submitted:
Source: Kelvin Chou
Yih-Shen Chen
I-Kang Fu
Paul Cheng
MediaTek Inc. No.1, Dusing Rd. 1, Hsinchu Science-Based Industrial Park,
Hsinchu, Taiwan 300, R.O.C.
Venue: Comment on IEEE m System Description Document:
On Session 10.8 Network Entry
Base Contribution: This is the base contribution
Purpose: To be discussed and adopted by TGm for the m SDD

2. Problem Description: Overhead in CDMA Initial / Periodic Ranging (1/2)
Procedures for the OFDMA-based ranging
The MS chooses randomly a Ranging Slot in a single frame
The MS chooses randomly a Ranging Code and sends it to the BS (as a CDMA code)
Upon successfully receiving a CDMA ranging code, the BS broadcast a ranging response message with the following properties:
Ranging Code index (8 bits)
Frame number (8 bits)
Time symbol reference (10 bits)
Subchannel reference (6 bits)
Shared knowledge between MS and BS
Ranging / BR opportunities
OFDMA-specific ranging response message encoding

3. Problem Description: Overhead in CDMA Initial / Periodic Ranging (2/2)
Shared knowledge is exchanged every time to identify anonymous RNG-RSP and anonymous bandwidth allocation in both initial ranging and periodic ranging
Anonymous RNG-RSP
Anonymous
bandwidth allocation

4. Proposed Solution: Hash Identity for Anonymous RNG-RSP / BW Allocation
Shared knowledge needs not be exchanged over the air
Can be verified by a shorter message derived from the shared knowledge
Let
A be frame number (8 bits)
B be ranging code index (8 bits)
C be subchannel reference (6 bits)
D be time reference (10 bits)
Encoding at BS
Decoding at MS
(10 bits)
A’(10 bits)
(10 bits)
(10 bits)
BS sends A’ (10 bits) instead of (A+B+C+D) to MS
Saved 22 bits

5. Performance Analysis: Hash Identity Collision (1/2)
Probability of hash identity collision
Less than 1% (5 users, 10-bit key)
Independent to the number of hash keys (number of XOR operations)
The more shared information, the more bits we save
Average number of contention users in a frame falls with this region

6. Performance Analysis: Hash Identity Collision (2/2)
Probability of hash identity collision
Less than 1% (5 users, 10-bit key)
Drops exponentially as key length increases

7. Performance Analysis: Hash Identity Collision Handling
Hash identity collision leads to collision of ranging request messages
Identical to the case of ranging code collision
BS may broadcast ranging status report to notify MSs and to expedite the start of the next round ranging
Ranging code collision handling
Hash collision handling

8. SDD Text Proposal
[Add the following blue text to the end of 10.8, Page 56, line 3.]
10.8 Network Entry
Network entry is the procedure by which an AMS finds and establishes a connection with the network. The network entry has the following steps:
– AMS synchronizes with the ABS via synchronization channel (SCH).
– AMS obtains necessary information e.g. ABS ID, NSP ID for initial network entry, and performs network selection.
– AMS starts ranging process.
– Authentication and registration process.
– AMS enters 16m network and sets up service flows.
Neighbour BSs search is based on the same downlink signals as initial network search (eg: preamble) except some information can be provided by serving ABS (eg: NBR-ADV). Network re-entry from such procedures as handover, idle mode exit and so on, is based on initial network entry procedure with certain optimization procedures.
The ABS shall respond to the AMS’ initial ranging code transmission by broadcasting a status indication message (e.g.: Decoding Status Bitmap) in a following predefined DL frame/subframe. The initial ranging related messages (e.g.: RNG-RSP and BW Grant) can be embedded linked to the corresponding bit of the status indication message to reduce overhead.
Upon successfully receiving a CDMA ranging code, the ABS broadcasts a ranging response message that advertises the hash identity derived from the received ranging code and the ranging slot information (OFDMA symbol number, subchannel, etc.) where the CDMA ranging code has been identified. This hash identity is used by the SS that sent the CDMA ranging code to identify the ranging response message that corresponds to its ranging request.