Month 1998 doc IEEE 802 11 02181 r

Month 1998 doc. : IEEE 802. 11 -02/181 r 1 802. 11 g Contention Period – Solution for Co-existence with Legacy Sunghyun Choi+, Olaf Hirsch*, Atul Garg*, Javier del Prado+ +Philips Research and *Philips Semiconductors Submission 1 John Doe, His Company

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Outline • Background • Analysis of using RTS/CTS for. 11 g ERP • 802. 11 g CP – a simple but efficient solution for co-existence • Revision made simple! – need to add only a single sentence into the draft Submission 2 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Assumptions • . 11 g and. 11 b STAs co-exist in a BSS. • BSS Basic Rate set is equal to or a subset of. 11 b DSSS/CCK rates. • Legacy. 11 b STAs may not correctly see a pure OFDM ERP frame as a busy channel. Submission 3 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Background • 802. 11 g/D 2. 1 - Using CCK-RTS/CTS to make. 11 b STAs set NAV during pure OFDM frame transmissions – Legacy Indication information element newly defined for the purpose • 02/051 r 0 -. 11 g and. 11 b collision avoidance via OFDM CP – Needed to add a new information element in beacons & some MAC operation changes Submission 4 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Comments on RTS/CTS • It is a plausible solution apparently! • But, this will lead to high overhead and reduce the maximum system throughput compared to the pure OFDM network. – See the next! • It turns out that fragmentation should not be used for MSDU transmitted at a pure OFDM ERP rate and protected by RTS/CTS. – See the next! • Have to minimize the usage of RTS/CTS !!! Submission 5 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Analytical Comparison • . 11 g two RTS/CTS options considered: – Long RTS: 2 Mbps rate & Long preamble (more realistic? ) – Short RTS: 11 Mbps rate & Short preamble (as assumed in 02/065) • Theoretical throughput analysis – Assuming one transmitter and one receiver – See next … Submission 6 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Transmission Time Comparison Preferred Choice Submission 7 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Theoretical Throughput Comparison Preferred Choice Submission 8 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 . 11 g Fragmentation Problem • RTS/CTS protect only the first fragment and ACK. • The subsequent fragments are not protected! Submission 9 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Complementary Solution • To reduce the usage of RTS/CTS … • 802. 11 g Contention Period (CP)! – Similar to OFDM CP of 02/051 r 0 … • . 11 g CP does not require any new information element!!! • Moreover, it can be achieved using a recommended practice as using CCK-RTS/CTS is according to 802. 11 g/D 2. 1. Submission 10 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 802. 11 MAC – CFP and CP • • Superframe = CFP and CP CFP starts with a beacon transmission PCF during CFP and DCF during CP (802. 11 e HCF during both CFP and CP) Submission 11 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 PCF Element and Frames • CF Parameter Set element • CF-END and CF-END + CF-Ack control frames – RA is broadcast group address Submission 12 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 PCF Operation during CFP • NAV is reset if CF-END (+ CF-ACK) is received • So, CFP ends with a CF-END (+ CF-ACK) Submission 13 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 . 11 g CP – Contention by. 11 g STAs Only! • . 11 g CP starts with a CF-END (+ CF-ACK) transmitted at an ERP rate Submission 14 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 During. 11 g CP … • . 11 g CP is part of CFP to. 11 b STAs!!! • So, . 11 g STAs do not need to use protection mechanisms (such as RTS/CTS and no fragmentation) during. 11 g CP • Is it true? Not really. See the next! Submission 15 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Collision Example • The. 11 g ERP frame should have been protected with CCK-RTS/CTS! Submission 16 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Solution • . 11 g STAs should start using protection mechanisms beginning T(. 11 b CP start) – T_extra, not beginning T(. 11 b CP start) Submission 17 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Two Ways to Determine T_extra 1. T_extra = maximum transmission time of an MSDU at a. 11 g ERP rate – 4. 8 msec for 2304 octect MSDU transmitted at 6 Mbps with 11 fragments 2. T_extra = duration of a pending frame exchange sequence, which cannot be finished by the upcoming T(. 11 b CP start) – Should be smaller than 4. 8 msec – Can maximize. 11 g CP advantage at the cost of duration calculations! Submission 18 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Why This Mechanism Works? • CF-Awareness is not optional !!! • According to 802. 11 -1999, 802. 11 STAs shall – Understand CF Parameter Set elements – Preset NAV at Target Beacon Transmission Time (TBTT) when a CFP is scheduled to start – See 9. 3. 2. 2 & Annex A. 4. 4. 1 PICS PC 3. 1 • Reception of CF-END (+ CF-ACK) shall be supported by 802. 11 STAs – See Annex A. 4. 4. 2 PICS FR 16 & RF 17 Submission 19 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 What AP Needs to Do? • Include CF Parameter Set information element even if no need for CFP – When CFP is not actually needed, a CF-END follows a beacon with a SIFS time gap (or PIFS time gap in case of 802. 11 e). • Transmit CF-END or CF-END+CF-ACK at one of ERP mandatory rates Submission 20 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 What. 11 g STA Needs to Do? • When Bit 1 of Legacy Indication element is set to one, protection mechanisms are used only during. 11 b CP and the last part of. 11 g CP. • The length of the last part of. 11 g to use protection mechanisms can be determined according to one of two ways explained earlier. Submission 21 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Single Change from 802. 11 g/D 2. 1 • 802. 11 b Clause 9. 6 reads: “All frames with multicast and broadcast RA shall be transmitted at one of the rates included in the BSS basic rate set, regardless of their type or subtype. ” • Add the following the above sentence: “For the Extended Rate PHY, control frames of subtypes CF-END and CF-END + CF-ACK may be transmitted at one of the Extended Rate PHY (ERP) mandatory rates irrespective of the BSS basic rate set. ” Submission 22 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Simulation Results Submission 23 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 OPNET Simulation Model • Revised our 11 b model • Supports 2 OFDM – 11 g modulations (24 and 6 Mbps) + 4 11 b modulations. • Slight change in the MAC model. Submission 24 S. Choi, et al. , Philips

March 2002 • • doc. : IEEE 802. 11 -02/181 r 1 Simulation Scenarios 8 stations : 4. 11 b and 4. 11 g Same load per STA – Network overloaded • 11 g stations: – Data + Ack at 24 Mbps – RTS/CTS transmitted using 11 b – 2 Mbps with long preamble • 11 b stations (long preamble): – Data at 11 Mbps – Control frames at 2 Mbps Submission 25 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Simulation Scenarios 1) DCF: – – 11 g stations use RTS/CTS always Beacon interval = 100 ms 2) 11 g_CP_11 b_CP – – – – Submission Beacon interval = 100 ms. CFP_Max_Perido (in the beacon) = 50 ms Beacon transmitted at 2 Mbps CF-END transmitted right after the beacon at 24 Mbps so 11 b stations don’t receive it 11 g CP: only 11 g stations contend for the medium. RTS/CTS not used 11 b CP: both 11 g and 11 b stations contend for the medium. 11 g stations use RTS/CTS T_extra = 5 ms 26 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Simulation Scenarios 3) 11 g_CP_11 b_CP_T_extra_adjusted: – Same scenario as (2). – The T_extra is adjusted according to the duration of each frame Simulations results in next slides are for a frame size of 1500 bytes Submission 27 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Aggregated Throughput Submission 28 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 2 nd simulation: 11 b traffic starts at 30 seconds Note: Although there is no 11 b traffic, the 11 g stations keep using RTS/CTS (always in the first scenario, during the 11 b CP in the 2 last scenarios) Submission 29 S. Choi, et al. , Philips

March 2002 doc. : IEEE 802. 11 -02/181 r 1 Aggregate Throughput Submission 30 S. Choi, et al. , Philips