doc.: IEEE 802.11-09/0364r0

Submission

March 11, 2009

JT Chen et al (Ralink Technology)Slide 1

Comments on AOA and AOD Selection for a Multi-User SDMA Network

Date: 2009-3-11

Authors:

Name Affiliations Address Phone email

Jiunn-Tsair Chen Ralink Technology

5F, No.36, Taiyuan St. Jhubei City, Hsinchu County 302, Taiwan

886-3-5600868 ext 1700

jt_chen@ralinktech.com.tw

Cheng-Hsuan Wu Ralink Technology

5F, No.36, Taiyuan St. Jhubei City, Hsinchu County 302, Taiwan

886-3-5600868 ext 1707

cs_wu@ralinktech.com.tw

Chun-Hsien Wen Ralink Technology

5F, No.36, Taiyuan St. Jhubei City, Hsinchu County 302, Taiwan

886-3-5600868 ext 1706

ch_wen@ralinktech.com.tw

doc.: IEEE 802.11-09/0364r0

Submission

March 11, 2009

JT Chen et al (Ralink Technology)

Outline

• Problem Description

• Current Proposal

• What Need to be Randomized

• What NOT to be Averaged Over

• Deterministic AoA and AoD in Test Cases

• Conclusions

• Suggestions

doc.: IEEE 802.11-09/0364r0

Submission

March 11, 2009

JT Chen et al (Ralink Technology)

Problem Description• In SDMA systems, multiple STAs are receive/transmit data

streams simultaneously. Channel parameters of cluster AoA/AoD of each STA is crucial in deciding its degree of difficulties of effective transmit beam-forming at the AP.

• On which there is consensus– AoA/AoD should be different for different STAs– Reuse the AS of each transmit/receiver channel path clusters– Reuse the number of clusters and PDP of each cluster

• On which there is no consensus– Identical AoA/AoD offsets, or not, for different clusters in the channel to

the same STA– AoA/AoD should be random, pseudo-random, or deterministic– The distribution of the AoA/AoD offsets, uniform distributed or whatever

other distributed over what range– System performance should be averaged, or not, over the distribution of

AoA/AoD offsets

doc.: IEEE 802.11-09/0364r0

Submission

March 11, 2009

JT Chen et al (Ralink Technology)

• Identical AoA/AoD offsets, or not, for different clusters in the channel to the same STA

Identical• AoA/AoD should be random, pseudo-random, or

deterministic

Pseudo-random • The distribution of the AoA/AoD offsets, uniform

distributed or whatever other distributed over what range

Uniform, over a range of Tx: Rx:• System performance should be averaged, or not, over the

distribution of AoA/AoD offsets

It should

Current Proposal

30o 180o

doc.: IEEE 802.11-09/0364r0

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March 11, 2009

JT Chen et al (Ralink Technology)

• Rotation is in sync among clusters of the same users, and/or some users• Average over a very small set of network scenarios• For example, it cannot test the scheduling algorithm taking advantage of multi-user diversity due to rank

deficiency of the channels to some users, since all users enjoy full rank simultaneously• Easily open to criticism from outside TGac

– An imaginary channel, non-realistic– Lack of in-depth technical consideration

Current Proposal, An Example – Channel D

doc.: IEEE 802.11-09/0364r0

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March 11, 2009

JT Chen et al (Ralink Technology)

• A set of parameters with different combinations of practical values will result in very different outcomes

• For example– Noise time samples in a communication system, Yes

– Fading amplitude of multi-paths in a wireless channel, Yes

– Error correction codebooks, No, not practical

– Pseudo scrambling bits, No, same performance outcome

– Raw data bits, Yes

• In extending from the SU 11n channel model to MU TGac channel model, what needs to randomized?– PDPs among multi-users, Probably Not

– ASs among multi-users, Probably Not

– Cluster AoAs/AoDs among multi-users, Certainly Yes

What Need to be Randomized

doc.: IEEE 802.11-09/0364r0

Submission

March 11, 2009

JT Chen et al (Ralink Technology)

• The control parameters that remain almost unchanged within the time/frequency/distance range defined by whatever user experience

• For example– Noise time samples in a communication system, Yes– Frequency selectivity or delay spread over a narrow-band communication

link, No, not in the frequency range– Different Test-Cases, No– 11n channel model A-F, No

• In extending from the SU 11n channel model to MU TGac channel model, what not to be averaged over?– Spatial correlation during a time period long enough to cause customer

complaints whenever system performance is bad, Certainly No– Cluster AoAs/AoDs among multi-users, Certainly No

• In conclusion, Cluster AoAs/AoDs are parameters we should randomize, but not average over.

What NOT to be Averaged Over

doc.: IEEE 802.11-09/0364r0

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March 11, 2009

JT Chen et al (Ralink Technology)

Deterministic AoA and AoD in Test Cases

• We propose to adopt different AoAs/AoDs values in different Test Cases– Initial randomness to reflect the specific purpose of the Test Case to

test against some system design gains.– Remain deterministic throughout the test case which a performance

outcome is exclusively reported for.

• The assignment of the AoAs/AoDs should – Be based on the Usage Models so as to remain practical– Covers typically-simple network scenarios to assure its feasibility– Covers typically-tough network scenarios to distinguish the quality of

different algorithms, and to assure its robustness

doc.: IEEE 802.11-09/0364r0

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March 11, 2009

JT Chen et al (Ralink Technology)

Modification in MATLAB Code• Parameter definition

– In example_MIMO.m, define AoD_Offset(transmitter_index, cluster_index) AoA_Offset(receiver_index, cluster_index) for all the transmitters and all the receivers. Call IEEE_802_11_Cases.m with one row of either matrix each time.

– In IEEE_802_11_Cases.m, define AoD_Offset(cluster_index) and AoA_Offset(cluster_index) to obtain the corresponding parameters

• MATLAB Code Segment in will get MIMO channels

doc.: IEEE 802.11-09/0364r0

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March 11, 2009

JT Chen et al (Ralink Technology)

Conclusions• It is too early for a first-cut document on TGac channel

model before – We look into the channel characteristics that can test the merit of

outstanding algorithms on different aspects

– We get a clear sense of direction on what we are really doing

• Reversal of incorrect decisions in the early stage could suck in a lot of research efforts and is certainly painful

doc.: IEEE 802.11-09/0364r0

Submission

March 11, 2009

JT Chen et al (Ralink Technology)

Suggestions• Before the next session, everyone is welcomed to suggest

AoDs/AoAs plus whatever other necessary parameters in test cases which favor the algorithms you are currently developing

• We then

– take the common part getting rid of the redundance,

– remove the impractical part, and then

– forge them into a document to cover parameters describing all the test cases