IMPLEMENTING CHANNEL ESTIMATION ALGORITHMS ON HARDWARE

Sridhar Rajagopal, Suman Das and Joseph R. Cavallaro

1.Multiuser Channel Estimation1.Multiuser Channel Estimation 5.Task Decomposition5.Task Decomposition

9 10 11 12 13 14 150

0.5

1

1.5

2

2.5

3

x 105

Number of Users

Dat

a R

ates

Data Rates for Different Levels of Pipelining and Parallelism

(Parallel A) (Parallel+Pipe B)

(Parallel A) (Pipe B)

(Parallel A) B

A B

Sequential A + B

Data Rate Requirement = 128 Kbps

3 .Base-station Receiver3 .Base-station Receiver

The Wireless ChannelThe Wireless Channel

Direct PathReflected Paths

Noise + MAI

User 1

User 2

Base Station

2.Third Generation Communication Systems2.Third Generation Communication Systems

6. Exploiting Pipelining and Parallelism6. Exploiting Pipelining and Parallelism

7. Meeting Real-Time Requirements7. Meeting Real-Time Requirements

Multiple Users

Channel

Estimation

Multiuser

Detection

DecoderData

Pilot

Demod-ulator

Antenna

Decision Feedback

MUX

Detected Bits

+

Delay

MUX

d

b (known)

8.Real-Time Implementation8.Real-Time Implementation

VLSI DSP FPGA High Performance Processors

DSP + FPGA

Joint Work with

Praful Kaul (UIUC)

Parthasarathy Ranganathan

Dr. Sarita Adve (UIUC)

SpreadingFactor

Number ofBits / Frame

Data RateRequirement

4 10240 1024 Kbps32 1280 128 Kbps

256 160 16 Kbps

4. DSP Implementation4. DSP Implementation

K

1

Block IV Matrix Products

A0HA1

AHrA0HA0

O(DK2Me)

1

K

Block III

A1HA1

data

d

• TI TMSC6701, projected at 250 MHz.

• 1953 cycles available for detection of 1 bit

assuming data rate of 128 Kbps.

• In-depth profiling to find bottlenecks.

• Multiuser Detection

– needs to performed continuously to meet data

rate requirements

• Channel Estimation

– can be updated less frequently

• Single DSP does not meet real-time requirements

• Multiuser Detection - Bottleneck!

• Multiuser Channel Estimation

– Need to know the Channel for proper detection

– Delays and Amplitudes of each user and each path

• Send sequence of known bits (Pilot / Preamble)

– Pilot Code-Multiplexed with Data

– Pilot Time-Multiplexed with Data

• Multiuser Detection

– Use knowledge of channel for reliable detection

•Multiple Users•Multiple Access Interference

•Multipath Delays

•Fading

•Additive White Gaussian Noise

Channel Effects

• Multiuser Channel Estimation Methods

– Subspace

– Maximum Likelihood

• Joint Estimation and Detection

– Computationally Efficient

– Better BER Performance

• W-CDMA - Wideband CDMA (5 MHz)

• 3G Communication Systems

–Integrating Multimedia Capabilities

–Quality of Service (QoS)

–Multi-rate Services

–Higher Data Rates

• 2048,384,144 Kbps

• N - Spreading Code Length

• K - Number of Users

• A - [A0 A1] - Channel Estimate

• D - Multiuser Detection Window

• r - Received bits of K users

– Can be Data or Pilot (with

interference/fading)

• b - Known Pilot bits at the receiver

• d - Detected Data bits

• Data’ - Data synchronized with d

Parameters

Accelerating the blocks in Multistage Detection

to meet real-time requirements.

Graph shows the data rates achieved by different levels

of acceleration for multiuser detection.

Block I Block II Block III

Inverse

Correlation Matrices (Per Bit)

Rbr

O(KN)RbbAH = Rbr

O(K2N)

Multistage

Detection

(Per Window)b

pilot

data

M

U

X

d

data’ M

U

X

RbbAH = Rbr

O(K2N)

O(DK2Me) d

Rbr

O(KN)

Rbb

O(K2)

Matrix Products

A0HA1

O(K2N)

AHr

O(KND)

A1HA1

O(K2N)

A0HA0

O(K2N)

Block IV

Multiuser Detection

Channel Estimation

Time

Task A Task B

Task ATask B