Abdul-Aziz .M Al-Yami Abdul-Aziz .M Al-Yami Khurram MasoodKhurram Masood

Case Study: Phase III Transmitter Receiver SimulationTransmitter Receiver Simulation

Physical Layer (PHY)Physical Layer (PHY)

The standard specifies the following four PHYs:1. An 868/915 MHz direct sequence spread spectrum (DSSS) PHY

employing binary phase-shift keying (BPSK) modulation2. An 868/915 MHz DSSS PHY employing offset quadrature phase-

shift keying (O-QPSK) modulation3. An 868/915 MHz parallel sequence spread spectrum (PSSS) PHY

employing BPSK and amplitude shift keying (ASK) modulation4. A 2450 MHz DSSS PHY employing O-QPSK modulation

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Frequency bands and data ratesFrequency bands and data rates

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4

Frequency bands and data ratesFrequency bands and data rates

2.4 GHz PHY – channels 11-265 MHz

2.4 GHz 2.4835 GHz

902 MHz 928 MHz

Channels 1-10

868.3 MHz

Channel 0

868 / 915 MHz PHY

2 MHz

5

PHY – 2.4 GHz ModePHY – 2.4 GHz Mode

• Each symbol (i.e. 4 bits) is represented by one of 16 32-chip sequences

• First 8 sequences are cyclic shifts of one 32-chip sequence, last 8 are cyclic shifts of another sequence (see next slide)

6

……

PHY – 2.4 GHz ModePHY – 2.4 GHz Mode

7

PHY – 2.4 GHz ModePHY – 2.4 GHz Mode

• Chip modulation is offset-QPSK, in which the Q-branch signal is delayed by one chip period (Tc) with respect to the I-branch signal

• Pulse shape is half-sine with period 2Tc

8

PHY – 2.4 GHz ModePHY – 2.4 GHz Mode

Offset-QPSK with half-sine pulse shaping

9

PHY – 868/915 MHz ModePHY – 868/915 MHz Mode

• Raw bits are differentially encoded– XOR between current bit and the previous encoded bit

• Each coded bit mapped to a 15-chip PN sequence– Zero to 1 1 1 1 0 1 0 1 1 0 0 1 0 0 0– One to 0 0 0 0 1 0 1 0 0 1 1 0 1 1 1 (zero’s complement)

• BPSK modulation with raised cosine pulse shaping with roll-off = 1.0 (100 % excess bandwidth)

2450 MHz DSSS PHY with O-QPSK2450 MHz DSSS PHY with O-QPSK

A 2450 MHz DSSS PHY employing O-QPSK modulation provides250 kbps data rate

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BER vs SNRBER vs SNR

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0 1 2 3 4 5 610

-5

10-4

10-3

10-2

10-1

EbN0

BE

R2450 MHz band O-QPSK PHY at 250kb/s

869/915 MHz DSSS PHY with BPSK869/915 MHz DSSS PHY with BPSK

868/915 MHz BPSK PHY, provides 20 kb/s in the 868 MHz band and 40 kb/s in the 915 MHz band

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BER vs SNRBER vs SNR

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0 1 2 3 4 5 6 7 8 9 1010

-5

10-4

10-3

10-2

10-1

EbN0

BE

R868 MHz band BPSK PHY at 20kb/s

Semi-analytic Simulation (No ISI)Semi-analytic Simulation (No ISI)

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0 2 4 6 8 10 12 14

0.04

0.045

0.05

0.055

0.06

0.065

x-y

cros

scor

rela

tion

Computed Delay

Delay Estimation

Semi-analytic Simulation (No ISI)Semi-analytic Simulation (No ISI)

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0 5 10 15 20 25 30 35-20

-10

0

10

20D/Q EYE DIAGRAM

Sample Index

Dire

ct

0 5 10 15 20 25 30 35-1

-0.5

0

0.5

1

Sample Index

Qua

drat

ute

Eye diagram

Semi-analytic Simulation (No ISI)Semi-analytic Simulation (No ISI)

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0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100000

1

2

3

4

5

6

7

8

9Estimate of Noise Bandwidth of Receiver

Samples

Var

ianc

e E

stim

ate

at D

ecis

ion

Met

ric

Noise estimation

Semi-analytic Simulation (No ISI)Semi-analytic Simulation (No ISI)

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-10 -8 -6 -4 -2 0 2 4 6 8 1010

-6

10-5

10-4

10-3

10-2

10-1

100

Ideal and Measured System Performance

SNR (Eb/No)

Bit

Err

or R

ate

Ideal BPSK

SA ResultBER vs SNR

Semi-analytic Simulation (with ISI)Semi-analytic Simulation (with ISI)

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Delay Estimation

8 10 12 14 16 18 20 22

0.04

0.045

0.05

0.055

0.06

0.065

x-y

cros

scor

rela

tion

Computed Delay

Semi-analytic Simulation (with ISI)Semi-analytic Simulation (with ISI)

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Eye diagram

0 5 10 15 20 25 30 35-20

-10

0

10

20D/Q EYE DIAGRAM

Sample Index

Dire

ct

0 5 10 15 20 25 30 35-1

-0.5

0

0.5

1

Sample Index

Qua

drat

ute

Semi-analytic Simulation (with ISI)Semi-analytic Simulation (with ISI)

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0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100000

1

2

3

4

5

6

7

8

9Estimate of Noise Bandwidth of Receiver

Samples

Var

ianc

e E

stim

ate

at D

ecis

ion

Met

ric

Noise estimation

Semi-analytic Simulation (with ISI)Semi-analytic Simulation (with ISI)

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BER vs SNR

-10 -8 -6 -4 -2 0 2 4 6 8 1010

-6

10-5

10-4

10-3

10-2

10-1

100

Ideal and Measured System Performance

SNR (Eb/No)

Bit

Err

or R

ate

Ideal BPSK

SA Result