Feasibility of Coordinated Transmission for HEW

1. Feasibility of Coordinated Transmission for HEW Date: 2013-09-18 Authors: Yunzhou Li, Tsinghua Univ.

2. Abstract • This presentation discuss the feasibility of using coordinated transmission between adjacent APs for future WLAN networks. • As a similar technique, CoMP in LTE has been introduced briefly. • The potential gain derived from coordinated transmission has been analyzed, by comparing with LTE CoMP and coordinated transmission in WiFi and referring the experiment results. • Some simple coordinated schemes have been introduced. Yunzhou Li, Tsinghua Univ.

3. Background &Motivation • With the increase of AP density, the inter-BSS interference will be the dominant obstacle for increase of area throughput. • It is very difficult to work well If there existed a good path between two adjacent APs due to DL-UL interference between the two APs. • Therefore, effective technologies and strategies have been proposed to deal with inter-BSS interference in HEW. Yunzhou Li, Tsinghua Univ.

4. The Feasibility of Coordinated Transmission • As showed in the figure, Access Controller (AC) are widely used in operator deployed Wi-Fi networks • AC can play a role of controller of coordinated transmission between adjacent APs

5. The Feasibility of Coordinated Transmission • Enterprise is evolving towards a cloud-based model • No longer files and information are stored on local machines • Mobile access to cloud is expected to increase with the increase of smart mobile devices. Enterprise WiFi 11-13-0098-00-0wng-802-11-looking-ahead-to-the-future-part-II Yunzhou Li, Tsinghua Univ.

6. Coordinated Multi-Point (CoMP) transmission and reception In LTE • Joint Transmission (JT) • Simultaneous data transmission from multiple points (part of or entire CoMP cooperating set) to a single UE or multiple UEs in a time-frequency resource • Dynamic point selection (DPS)/muting • Data transmission from one point (within the CoMP cooperating set) in a time-frequency resource • Coordinated Scheduling/Beamforming (CS/CB) • Data for an UE is only available at and transmitted from one point • scheduling/beamforming decisions are made with coordination among points corresponding to the CoMP cooperating set. 3GPP TR 36.819 Coordinated multi-point operation for LTE physical layer aspects Yunzhou Li, Tsinghua Univ.

8. The Difference between TD-LTE and WiFi for Coordinated Transmission • In cellular systems of TD-LTE, all the eNBs are synchronized in symbol and slot • Whereas each AP in Wi-Fi systems decide to transmit/receive according to its situation and don’t take care of other adjacent AP’s TX/RX. • The AP will transmit if it can detect the channel and find the channel is idle or the adjacent AP's signal is below the CCA level. • In addition, the deployment of eNB are chosen base on well-planning, which is very different from selection of AP’s position. Yunzhou Li, Tsinghua Univ.

9. The Difference between TD-LTE and Wi-Fi for Coordination Transmission • Besides, there is a significant difference in use of time and frequency block between cellular and Wi-Fi. Yunzhou Li, Tsinghua Univ.

10. Some Coordinated Transmission Schemes • Integrated coordinated transmission mechanism with Wi-Fi networks • All the time domain resource is divided into two categories: Coordinated TX/RX Intervals(CTRI) and Non-Coordinated TX/RX Intervals(NCTRI) which is scheduled and decided by coordination controller according to the amount of STA and their distribution • CTRI is like the mechanism of DMA or Interrupt in computer system. Yunzhou Li, Tsinghua Univ.

11. Some Coordinated Transmission Schemes • Coordinated power allocation • The scheme of AP selection is one special case of coordinated power allocation. Yunzhou Li, Tsinghua Univ.

12. Some Coordinated Transmission Schemes • Coordinated frequency band allocation: similar to fractional frequency reuse in LTE • Joint dynamic allocation of frequency and power • Which is the combining case of coordinated power allocation and coordinated frequency band allocation Yunzhou Li, Tsinghua Univ.

13. Some Coordinated Transmission Schemes • Joint Transmission based one joint precoding • like SU-MIMO / MU-MIMO in 802.11ac • The combing channel is and the precoding matrix is decided based on • MU-MIMO can be combined to the scheme • JT need high-resolution synchronization in time and frequency among the adjacent APs, which can be implemented by CPRI / IEEE 1588, etc. Coherent Yunzhou Li, Tsinghua Univ.

14. Experiment of Multi-AP for Dense WLAN • Each STA can detect multiple APs within its received range.

15. Experiment of Multi-AP for Dense WLAN • Strategies: • In UL, multi-AP demodulate the STA’s signal simultaneously and check it by CRC. • In DL, the controller chooses one AP from multi-AP as transmit point according to channel condition and load balance. StarEast

16. Experiment of Multi-AP for Dense WLAN • Combining with optimal physical carrier sensing(PCS), more 100% gain can be achieved in both UL and DL. UL DL Yunzhou Li, Tsinghua Univ.

17. Remarks on Coordination Gain • Although only about 15% gain from CoMP in LTE can be achieved, considerable gain from simple coordinated scheme has been showed in our experiment. • In our opinion, the possible reason is CoMP gain in LTE derived from the improved SINR for cell-edge UEs who are at low rates, so the contribution for the whole cell throughput is not considerable. • However, the gain from coordinated transmission in WLAN is from the decrease of collision and resulting in the increase of transmission opportunity. Yunzhou Li, Tsinghua Univ.

18. Summary • It is feasible for integrating coordinated transmission in to WLAN for HEW by extending the role of AC. • For analysis of potential gain, CoMP in LTE has been introduced briefly. • Further, the difference between TD-LTE and WiFi for coordinated transmission has been summed up and some simple coordinated scheme has been introduced. • Finally, the potential gain for HEW has been analyzed. Yunzhou Li, Tsinghua Univ.