System and method for reducing packet collisions in wireless local area networks

• US 7,801,104 B2
• Filed: 10/26/2006
• Issued: 09/21/2010
• Est. Priority Date: 10/26/2006
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Gaur, Sudhanshu
• Primary Examiner(s): Appiah; Charles N
• Assistant Examiner(s): Rideout; William F
• Application Number:
  US11/588,624
• Publication Number:
  US 20080101308A1
• Time in Patent Office: 1,426 Days
• Field of Search: 370/343, 370/338, 370/345, 455/450, 455/452.1
• US Class Current: 370/345
• CPC Class Codes: H04W 72/23 in the downlink direction of a wireless link, i.e. towards a terminal
• CPC Class Codes: H04W 74/0816 with collision avoidance
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A system (e.g., an AP or a STA) in a WLAN comprises slot information (e.g., slot association or slot bias information); a counter for counting slot numbers; and a medium access controller operative to monitor a wireless medium and to initiate transmission of a MAC frame during a current slot based an a distributed wireless access protocol (e.g., DCF or EDCA), on a current slot number (t) corresponding to the current slot as counted by the counter, and on the slot information. The medium access controller may initiate frame transmission when a backoff counter is zero and when t mod N=n_i (such that N=number of STAs, and n_i=assigned slot number). Alternatively, the medium access controller may initiate frame transmission when a backoff counter is zero and when a slot bias mechanism effecting a probability of access to the wireless medium is satisfied.

Claims

1. A system in an IEEE 802.11 a wireless local area network, comprising:

a counter for counting slot numbers; and

a storage device to store data corresponding to a channel access scheme providing access to a wireless network, said access scheme using a modulo partitioning backoff scheme providing a modulo partitioning backoff, said channel access scheme further providing traffic prioritization, wherein each transmitter is allowed channel access after a backoff counter becomes zero and a current slot number t satisfies the modulo condition;

t modulo N=n_i

where,

t=a current slot number where a slot count begins at zero after short interface space (SIFS) interval past medium busy,

N=total number of stations (STAs) in the wireless network,

n_i=a Unique ID assigned by the AP to each station (STA), and

wherein SIFS is shorter than distributed coordinated function interframe space (DIFS) and arbitrary interframe space (AIFS).

2. The system of claim 1, wherein said traffic prioritization is accomplished by using an arbitration interframe space (AIFS) interval defined on per-class basis, wherein multiple unique IDs, n_i, are assigned to different access classes (ACs) within the same STA.

3. The system of claim 2, wherein said modulo N is equal to number of STAs.

4. The system of claim 2, wherein said channel access scheme using a modulo partitioning backoff scheme further comprises:

a. setting backoff_counter=random (0, CW) and slot counter as t=0;

b. waiting SIFS duration after medium busy

c. waiting one slot and if slot is idle, setting t=t+1 and repeating until t=AIFSN[AC];

if slot is not idle, set t=0 and go to step (b);

d. waiting one slot and if slot is idle, setting backoff_counter=transmitting a packet if t modulo N=n_i;

if t modulo N≠

n_i, wait one slot, set t=t+1, and, if slot is idle, repeat until t modulo N=n_i;

if slot is not idle, return to step (b).

5. The system of claim 2, wherein said channel access scheme using a modulo partitioning backoff scheme further comprises:

a. setting backoff_counter=random (0, CW) and slot counter as t=0;

b. waiting SIFS duration after medium busy

c. waiting one slot and if slot is idle, setting t=t+1 and repeating until t=AIFSN[AC];

if slot is not idle, set t=0 and go to step (b);

d. waiting one slot and if slot is idle, setting backoff_counter=backoff_counter−

1, and t=t+1, and repeating until backoff_counter=0;

if slot is not idle set t=0 and go to step (b);

e. transmitting a packet with high probability (P_H) if t modulo N=n_i, and with low probability (P_L) if t modulo N≠

n_i;

if no transmission occurs, wait one slot, set t=t+1, and, if slot is idle, repeat step (e);

if slot is not idle, return to step (b).