Synchronization Requirements and Solutions for 802.11n Month 2002 doc.: IEEE 802.11-02/xxxr0 July 2004 Synchronization Requirements and Solutions for 802.11n Morgan H. Miki, John M. Kowalski Sharp Morgan H. Miki, John M. Kowalski, Sharp John Doe, His Company

July 2004 Problem: Consumer electronic devices figure prominently in 802.11n usage models. CE devices however, require tight synchronization to maintain high quality audio if multicasting is done. This presentation presents some results on the state of the art for synchronization in 11a, and recommendations to improve it for 802.11n. Without some solution in this regard, the user experience of CE over 802.11n may be compromised. Morgan H. Miki, John M. Kowalski

Clock Synchronization July 2004 1 Clock difference jitter Clock difference jitter: Depends on clock precision and how often TSs are distributed Tx clock: 20MHz ± 20ppm Rx clock: 20MHz ± 20ppm TS: Time Stamp TSF: Timing synchronization function TSF timer TSF timer TS Channel TS RX TX Packet detection jitter 3 Packet detection jitter: Depends on synchronization algorithm, PHY rate and PER Channel jitter 2 Channel jitter: Depends on the movement of stations (1ns jitter for 30cm) Clock synchronization is affected by Morgan H. Miki, John M. Kowalski

Clock Synchronization requirements July 2004 Clock Synchronization requirements Desired for stereo audio (professional level) [1] Acceptable for one receiver Acceptable for stereo audio[1] Synchronization jitter 10ms 1ms 100us 10us 1us 100ns 10ns 1ns 100ps 802.11a MPEG2: 500ns 1394: app 40ns Why improve 802.11 synchronization? HDTV/STDV/audio streams are 802.11n applications. The jitter generated by wireless link should be reduced at wireless level, to minimize overall delay. The effect is to make CSMA/CA behave more truly like a discrete time system. Technology has improved anyway since 11a was introduced. Morgan H. Miki, John M. Kowalski

Possible solution: July 2004 Add 8 byte 10ns unit Time Stamp in every QoS packet (Option) Example of implementation may use DLL (Delay locked loop) eP eQ ef TX TSF Timer TimeStamp + PHY/MAC processing time 1 / T KP eI KI 1 fRX Z-1 fTX Loop Filter RX TSF Timer rf Tx/Rx timer synchronization error jitter PHY/MAC processing time is the time between packet detection and MAC to output the Time Stamp for DLL Morgan H. Miki, John M. Kowalski

Simulation conditions July 2004 Simulation conditions Tx and Rx clock precision: 20 ppm Packet detection with legacy 11a preambles and PLCP. App. 10% PER @ 16QAM ¾ coding rate. This results in packet detection jitter of ±100ns. (video applications) Simulations with Channel B/D/E Channel jitter considered as 0ns i.e. no station mobility (1ns jitter/30cm). Interval between packets: 500us (max 30ms at high error rate region) Morgan H. Miki, John M. Kowalski

Simulation results (channel B) July 2004 Synchronization error jitter (ns) Jitter: < ±25ns Convergence time: 40s Time(s) Similar results for channel D/E Morgan H. Miki, John M. Kowalski

Comparison Mode Time to convergence Synchronization error jitter -- July 2004 Mode Time to convergence Synchronization error jitter 1us TS, TS in beacons, no DLL, 20ppm oscillator(11a) -- ±10us with DLL, 20ppm oscillator(11a) 20 min ±250ns 10ns TS, TS in beacons, with DLL, 20ppm oscillator 20min ±50ns 10ns TS, TS in every QoS packets, with DLL, 20ppm oscillator 40s ±25ns 10ns TS, TS in every QoS packets, with DLL, 1ppm oscillator 60s ±10ns Morgan H. Miki, John M. Kowalski

July 2004 Conclusions The use of 8 byte 10ns unit time stamp in all QoS packets should be considered as option. A great improvement from legacy 802.11 (10us to 25ns) can be achieved. Synchronization can be further improved to acceptable stereo audio level by using higher precision oscillators (10ns) Presently investigating the effects of synchronization when MIMO preambles, other information, other preamble formats, etc. are used. Morgan H. Miki, John M. Kowalski

July 2004 References [1] Julian Dunn: “Sample clock jitter and real-time audio over the IEEE1394 high performance serial bus”, Nanophon Limited Morgan H. Miki, John M. Kowalski