1Runcom Technologies Ltd. Submission Eli Sofer, Runcom February 2007 Doc.: IEEE802.22-07-0072r0 Slide 1 OFDMA Single Channel Harmonization IEEE P802.22

1Runcom Technologies Ltd.Submission Eli Sofer, Runcom

February 2007 Doc.: IEEE802.22-07-0072r0

Slide 1

OFDMA Single Channel Harmonization IEEE P802.22 Wireless RANs Date: 2007.8.02

Name Company Address Phone email Eli Sofer Runcom Technologies 2 Hachoma St., 75655

Rishon Lezion, Israel +972 3 9428892 [email protected]

Yossi Segal Runcom Technologies 2, achoma St. 75655 Rishon Lezion, Israel

+972 3 952 8440 [email protected]

Doron Ezri Runcom Technologies 2, achoma St. 75655 Rishon Lezion, Israel


Michael Erlichson

Runcom Technologies 2, achoma St. 75655 Rishon Lezion, Israel


Authors:

Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22.

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Slide 2

• Adequacy of CAZAC PN sequences• Attributes of PN sequences needed to support

WRAN deployment with Reuse factor 1/3• Partial simulations results on O-PUSC



Slide 3

Adequacy of proposed CAZAC scheme

• the PAPR of preamble is an important property. However, the preamble PAPR should be examined in view of the payload PAPR. That is, decreasing the Preamble PAPR beneath the expected payload PAPR would not lead to any advantage on the system level.

• The very low 1-2 dB PAPR suggested by the CAZAC approach would give almost no advantage over another series with PAPR in the vicinity of 4-5dB.

•Although the CAZAC waveforms are simple to generate (similarity to the sounding waveforms of the 802.16e) the decoding/reception complexity is extremely high. This is easy to show by means of comparison with BPSK modulated preamble. The estimation process begin with multiplying the incoming preamble (in the frequency domain) with a series of PN sequences (stored at the UT memory). Obviously, the multiplication of a digital series with a sequence of +1, -1 (BPSK) is far more attractive and simpler than the multiplication with a series of complex value numbers (suggested by CAZAC approach)

•



Slide 4

• CAZAC approach would imply a complex HW required to carryout a large number of complex multiplications ( the number is identical to number of pilots within the preamble). The negligible gain of CAZAC preamble on the system level does not justify the massive HW requirements.

• we recommend use of binary PN sequences.

Adequacy of proposed CAZAC scheme



Slide 5

Attributes of PN sequences needed to support WRAN deployment with Reuse factor 1/3 (use of aggregated channels)



Slide 6

In multi-cell deployment, the popular deployment is with Hexagon like cells. This allows the use of multiple different allocation within the cell (Reuse factor < 1) Reuse 1/3 deployment calls for decimated preamble with factor 3. This means that each segment uses a different set of pilot in Preamble (e.g. every 3n+k, K= 0,1,2). This preamble structure makes sure that the transmitted preamble by all 3 segments remain orthogonal (in the frequency domain)Simulation studies also show that in many scenarios (especially in the low CINR regime) the capacity of a cell with reuse less than 1 (e.g. 1/3) is higher than that in the elementary Reuse 1. We believe that similar deployment ideas will be predicted in the 80-2.22 standard. It is therefore important to adhere to the decimation with factor 3 for use as the 802.22 preambles.

Support for Channel aggregation



Slide 7

0 3 6 9 12 15 18 21 24 27 30 33

• Preamble with 3 repetitions (for three different sectors)

• 3 different Binary PN Sequences each shifted by one subcarrier (k= 0,1,2), allocated for three different sectors, supports resuse 1/3 (Aggregated channels)

• Interference mitigation among sectors, differentiation among sectors

Sub carriers

Preamble Binary PN Sequences

1 4 7 10 13 17 20 23 26 29 32

+1

-1



Slide 8

Seg

Seg Seg

Different PN sequence, each to one of the three sectors

Reuse 1/3



Slide 9

Coverage - Simulations

Multi Sector Coverage, 3 Sectors, 3 Frequencies, achieves 2.8Bits/s/Hz/Cell, 22.5Mbps/Sector



Slide 10

DL preamble and Ranging process



Slide 11

• The CDMA like synchronization is achieved by allocating several of the usable Sub-Channels for the Ranging process, the logic unit they consist is called a Ranging Sub-Channel.

• Onto the Ranging Sub-Channel users modulate a Pseudo Noise (PN) sequence using BPSK modulation

• The Base Station detects the different sequences and uses the CIR that he derives from the sequences for:

– Time and power synchronization

– Decide on the user modulation and coding

Ranging Process



Slide 12

• Subscriber Units at the Current OFDMA Symbol = 3

• Sub-Channels Allocated to Subscriber-Unit #1 = 12



• Number Of New Subscriber-Units Requesting Services = 3

All Subscriber-Units Suffer Different Multi-Paths and different Attenuation's

Effectiveness of DL Preamble and Ranging Example



Slide 13

• Constellation at the Base Station



Slide 14

• Users Separation



Slide 15

• User Estimation 1

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Constellation to Estiamte

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Estimated vec

Example - Results



Slide 16

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2


-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Estimated vec


Results



Slide 17

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2


-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Estimated vec


Results



Slide 18

0 20 40 60 80 100 120 1400

50

100

150

200

250

300Despreading on All Users

• Finding New Subscriber-Units Requesting Services, Using the Ranging Pilots (CDMA/OFDM Techniques)

Results

• Synchronization is achieved using DL preamble within accuracy of few micro seconds

• Preamble processing gain is 27dB, adding to that 9dB boosted pilots, overall 36dB

Time accuracy at UT (o.1 Microsecond/step)

Am

p



Slide 19

Simulations results on O-PUSC (Partial)



Slide 20

Scope

The purpose is to present performance of OPUSC scheme to various types of channel estimation methods. The simulations were ran with OPUSC frame structure for two profiles of WRAN channels.



Slide 21

Simulations parameters:

• Bandwidth =6MHz.• FFTSize=2048.• FEC Size=480;• Modulation =QPSK• CTC coding.• Coding rate=1/2.• Guard Interval=256.



Slide 22

OPUSC Frame Structure

Pilot

1 OPUSC Frame

2048 subcarriers



Slide 23

Additional assumptions:

• The simulation were ran without frequency shift and without phase noise.

• Since in the OPUSC scheme the pilots in each symbol are allocated not in all subcarriers, we used linear interpolation to perform channel estimation.



Slide 24

Channel parameters:

.

0.37Hz0.17Hz2.5 Hz0.13Hz00.1 HzDoppler

frequency

-20 Db-16 Db-22 Db-7 Db0-6 DbRelative

amplitude

117420-3Excess delay,

msec

Path6Path5Path4Path3Path2Path1 Profile 2

0.37Hz0.17Hz0.13Hz2.5 Hz0.1 Hz0Doppler

frequency

-19 Db-24 Db-22 Db-15 Db-7 Db0Relative

amplitude

211311830Excess delay,

msec

Path6Path5Path4Path3Path2Path1Profile 1



Slide 25

Channel parameters

The point spread function(PSD) of each tap

is defined as follows:

.,)/(1

1)(

2 dopdop

dop

fffff

fS



Slide 26

Reference Performance: Profile 1 (BER)

1 2 3 4 5 6 7 8 910

-7

10-6

10-5

10-4

10-3

SNR [dB]

10-2

10-1

100 OPUSC allocation QPSK 1/2 FEC 480 Profile 1

BE

R

3 symbols9 symbols15 symbols

Perfect channel



Slide 27

Reference Performance: Profile 1 (PER)

1 2 3 4 5 6 7 8 910

-4

10-3

10-2

10-1

100 OPUSC allocation QPSK 1/2 FEC 480

SNR [dB]

PE

R

3 symbols9 symbols15 symbols

Perfect channel



Slide 28


2 3 4 5 6 7 8 9 1010

-6

10-5

10-4

10-3

10-2

10-1


SNR [dB]

BE

R

3 symbols9 symbols



Slide 29


2 3 4 5 6 7 8 9 1010

-4

10-3

10-2

10-1


SNR [dB]

PE

R

3 symbols9 symbols



Slide 30

AMC 1x6 Parameters

2 3 4 5 6 7 8 9 1010

-4

10-3

10-2

10-1


SNR [dB]

PE

R

3 symbols9 symbols



Slide 31

Conclusions:

• The presented graphs show us that we have BER=1e-5 with SNR=9.5. In order to improve the channel estimation we suggest to aggregate number of frames (3 and 5). From the first graph we see that the aggregation of 5 frames improves the performance in approx. 3.5Db to compare with 1 frame and is close to the perfect channel performance.



Slide 32

Water filling conceptS

NR

Threshold

Threshold

Tiles spread

Channel behavior , different users

Tiles transmission on preferred frequencies

Different thresholds for different modulation schemes and coding rates

User1User

2



Slide 33

Conclusions

• Preamble with 3 reps is recommended (for 3 different segments), accommodating different deployment scenarios and multi-cell scenarios.

• PUSC simulation results so far are poor unless used tiles are transmitted in favorable CINR.

• The concepts presented by ETRI are almost identical to the transmission scheme (US & DS) of the 802.16.e. The changes are mostly semantic. We propose to adopt the concepts presented by ETRI (not necessarily the details.

Documents

1Runcom Technologies Ltd. Submission Eli Sofer, Runcom February 2007 Doc.: IEEE802.22-07-0072r0 Slide 1 OFDMA Single Channel Harmonization IEEE P802.22