Medium access control methods with quality of service and power management for wireless local area networks

• US 7,418,004 B2
• Filed: 12/28/2004
• Issued: 08/26/2008
• Est. Priority Date: 09/23/2004
• Status: Expired due to Fees

• Current Assignee: Institute For Information Industry
• Original Assignee: Institute For Information Industry
• Inventors: Chou, Zi-Tsan
• Primary Examiner(s): Nguyen, Duc
• Assistant Examiner(s): Win, Aung T
• Application Number:
  US11/022,866
• Publication Number:
  US 20060062181A1
• Time in Patent Office: 1,337 Days
• Field of Search: 370/311, 370/338, 370/449, 370/458, 370/329, 370/331, 455/435.1, 455/509
• US Class Current: 370/449
• CPC Class Codes: H04L 41/5003 Managing SLA; Interaction between SLA and QoS
• CPC Class Codes: H04L 41/5019 Ensuring fulfilment of SLA
• CPC Class Codes: H04W 74/06 using polling
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A MAC method has three procedures: a prioritization procedure, a collision resolution procedure, and a polling procedure. The prioritization procedure employs the handshaking method to ensure that a high priority station can join the polling list earlier than a low priority station. The collision resolution procedure employs a tree-splitting algorithm to ensure all active stations that underwent the prioritization period can join the polling list in a bounded time. In the polling procedure, the AP allocates the TXOP for each admitted station and schedules the transmission order of all admitted stations. In addition, the AP broadcasts the schedule information in the V-POLL frame. A power-saving station can wake up at the start of the contention-free period. To conserve power, on inspecting the V-POLL frame, if a PS station finds that it cannot transmit nor receive data frames during the polling period, then that station may return to the doze state.

Claims

1. A medium access control (MAC) method for applications with power conservation and quality-of-service requirements in a basic service set (BSS) of a wireless local area network (WLAN), comprising:

an optional registration procedure, which is coordinated by a access point (AP) to ensure that active stations can join a polling list from higher priority to lower priority; and

a mandatory polling procedure, which is coordinated by the AP to ensure that each polled station can transmit data frames according to a transmission opportunity (TXOP) and transmission order announced in a vector-list poll (V-POLL) frame;

wherein the MAC method is used in a contention-free period (CFP), wherein a BSS consists of the AP and a finite number of mobile stations, wherein a mobile station can be either in the active mode or in the power saving (PS) mode, wherein the AP broadcasts the V-POLL frame, and wherein the registration procedure is performed during a registration period and the polling procedure is performed during a polling period;

wherein the registration procedure comprises a prioritization procedure and a collision resolution procedure;

during the registration period, the AP performs the polling procedure once the AP recognizes that the overrun of the registration process violates the default TXOP value promised to any admitted station;

in the prioritization period, the AP performs the polling procedure when the AP has already enquired active stations with the lowest priority;

during the prioritization period, the AP performs the collision resolution procedure once the AP detects a COLLISION event, wherein the collision resolution procedure is executed in a form of handshaking to thus add one or more active stations into the polling list.

2. The MAC method of claim 1, wherein the prioritization procedure comprises:

(a) the AP broadcasting the priority enquiry frame, from higher priority to lower priority, to mobile stations within the BSS, wherein a priority enquiry (PE) frame includes at least a priority value or a possible range of priority values; and

(b) if an active station has a data frame or flow with a priority value either no less than that in the PE frame or belonging to the priority range in the PE frame, then that active station can send the priority response (PR) frame to the AP, wherein the PR frame includes at least the identifier of that active station, which is selected from the MAC address, association ID (AID), and other identifiable coding.

3. The prioritization procedure of claim 2, wherein according to the PR frame, the AP will perform one of the following two steps:

(c) if the AP did not receive any PR frame (IDLE event), then the AP decreases the priority value or shortens the priority range, and next performs the step (a);

(d) if the AP correctly received one PR frame (SINGLE event), then the AP adds the active station of that PR frame to the polling list, and next the AP decreases the priority value or shortens the priority range, and next performs the step (a);

(e) if two or more active stations replied PR frames to the AP (COLLISION event), then the AP starts to perform the collision resolution procedure.

4. The MAC method of claim 1, wherein the collision resolution procedure uses a tree-splitting algorithm to identify active stations that bring the COLLISION event during the prioritization period, comprising:

a registration enquiry step;

the AP broadcasts a registration enquiry (RE) frame to stations within the BSS, wherein the RE frame includes at least an address pattern; and

a registration response step;

if an active station whose identifier belongs to the address pattern in the RE frame, then the active station sends the registration response (RR) frame to the AP, wherein the RR frame includes at least the identifier of that active station.

5. The MAC method of claim 1, wherein during the registration period, each active station can propose its demanded TXOP (dTXOP) in a current polling period and a required guaranteed TXOP (gTXOP) during the connection lifetime;

further, each polled station can piggyback a dTXOP value required in the next polling period with the data frame.

6. The MAC method of claim 1, wherein during the registration period, the AP periodically announces the RACT (remaining available channel time) of the contention-free period;

the active station whose default TXOP (the minimum of dTXOP and gTXOP) is greater than RACT can either adjust its dTXOP or gTXOP, or abort the contention in the remaining registration period and wait for the next CFP.

7. The MAC method of claim 1, wherein the polling procedure further comprises:

a channel time allocation procedure;

the AP allocates a TXOP value for each yet-to-be-polled station;

a transmission order arrangement procedure;

the AP arranges the transmission order for each yet-to-be-polled station;

a V-POLL frame broadcast step;

the AP broadcasts the V-POLL frame to stations within the BSS, wherein the V-POLL frame contains a vector list and each vector is composed of a yet-to-be-polled station, its intended receiver, and a granted TXOP; and

a data transmission procedure;

all polled stations sequentially transmit data frames according to the indication of the V-POLL frame.

8. The MAC method of claim 1, wherein a power saving (PS) station wakes up at the start of the contention-free period and stays in the awake state;

on inspecting the V-POLL frame, a PS station that can neither transmit nor receive data frames during the polling period returns to the doze state.

9. The MAC method of claim 7, wherein the data transmission procedure further comprises:

a fault detection step;

when the AP detects that a polled station does not respond to the V-POLL frame, the AP then resends the new V-POLL frame containing the remaining un-transmitted stations on the polling list.

10. The MAC method of claim 7, wherein in the channel time allocation procedure, the AP allocates a TXOP value for each admitted station according to its dTXOP and gTXOP.

11. The MAC method of claim 7, wherein in the transmission order arrangement procedure:

the AP schedules the transmission order for each yet-to-be-polled power-saving station, based on the total time required in transmitting and receiving during the polling period, in an increasing order.

12. The MAC method of claim 7, wherein in the data transmission procedure, if an admitted station desires to leave the polling list, then that station can piggyback a leave information with the data frame to notify the AP;

when the AP receives the leave information, it can remove that station from the polling list.

13. The MAC method of claim 9, in the fault detection step, if a polled station does not respond to the V-POLL frame for K consecutive contention-free periods, then the AP removes the station from the polling list, wherein K is an integer defined by the AP.