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Sequence design for parallel ACK. Authors:. Date: 2012-01-09. Abstract. Proposed Contention-Free Probe and Pull MAC for large network [1] Parallel ACK is crucial to the proposed Probe and Pull MAC High level idea of physical layer support for parallel ACKs for Probe and Pull MAC.

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sequence design for parallel ack
Sequence design for parallel ACK

Authors:

  • Date:2012-01-09

Taejoon Kim, Nokia

abstract
Abstract
  • Proposed Contention-Free Probe and Pull MAC for large network [1]
  • Parallel ACK is crucial to the proposed Probe and Pull MAC
  • High level idea of physical layer support for parallel ACKs for Probe and Pull MAC

Taejoon Kim, Nokia

parallel ack mechanism 1
Parallel ACK Mechanism [1]
  • STAs with data to send transmit ACKs concurrently (in time-aligned manner)
  • Parallel ACKs imply inevitable interference

Need method for resolving parallel ACKs

SIFS

SIFS

Pull

Probe

AP

ACK

STA 1

has data to send

ACK

STA 2

has data to send

ACK

STA K

has data to send

Taejoon Kim, Nokia

sequences to resolve parallel acks
Sequences to Resolve Parallel ACKs
  • Separate STAs in code-domain
  • Consider combination of code- and time-domain

Code-domain

Sequence ID is used to identify STA ID

Time-domain

Use sequence ID & time slot instance to identify STA ID

Code-domain

Time slot 1

Time slot 2

Time slot 3

Taejoon Kim, Nokia

zadoff chu zc sequence as a signature
Zadoff-Chu (ZC) Sequence as a Signature
  • Zadoff-Chu (ZC) sequence

,

  • Zero cyclic autocorrelation
  • Minimum cyclic cross-correlation
      • If is relative prime with ,
  • Amount of cyclic shifts and/or root values indicate sequence ID

root of sequence

length of sequence

Cyclic shift by k

  • If is prime, the condition is guaranteed

Taejoon Kim, Nokia

physical parallel acks
Physical Parallel ACKs
  • Each STA maps ZC sequence (pre-assigned to STA) to OFDM subcarriers, perform IFFT, add cyclic prefix, and transmits it
  • Sum of ACKs arrives at AP with delays

One OFDM symbol per time slot

One time slot

TRTT: max round-trip time, e.g.,

AP

ACK_STA1+ACK_STA2

STA in 1km range

TFFT

TMD

TMD: max multipath delay, e.g.,

ACK_STA1

for urban micro (RMS DS = 0.25us for SCM Umi [2])

TRTT

ACK_STA2

TCP: CP duration, e.g., 8us =+

TCP

TGI

TRTT

  • : guard interval, e.g,

FFT window

FFT window

FFT output

Detect multiple STAs

Taejoon Kim, Nokia

parallel ack detection at ap
Parallel ACK Detection at AP
  • Non-coherent detection
  • De-correlation(matched filter)-based threshold detection
  • Use of cyclic shifted ZC sequences enables efficient frequency domain implementation

Taejoon Kim, Nokia

simulation setup
Simulation Setup

Taejoon Kim, Nokia

simulation results
Simulation Results

Taejoon Kim, Nokia

conclusions
Conclusions
  • High level framework for Physical Parallel ACK: Combination of code- and time-domain multiplexing, use of Zadoff-Chu sequence, time slot structure
  • Simulation results demonstrate robust detection capability for Parallel ACK

Taejoon Kim, Nokia

references
References
  • [1] 11-11-1512-00-00ahr4-mac-consideration-for-802.11ah
  • [2] J. Salo et al., “3GPP Spatial Channel Model,” [Online] Available: http://www.tkk.fi/Units/Radio/scm/

Taejoon Kim, Nokia