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Wireless Mesh Networks: First part: Point to point links of wireless mesh nodes based on MIMO UWB-IR technology.

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slide1

Wireless Mesh Networks:First part:Point to point links ofwireless mesh nodes based on MIMO UWB-IR technology

3-rd Workshop of WOMEN Project

University of Rome “Sapienza”, INFOCOM Dept. (Faculty of Engineering)

Rome January 19-th, 2007

outline
Outline

System model: main characteristics

Derivation of the MIMO UWB-IR Co-Decoder

Performance of the MIMO UWB-IR Co-Decoder

Main aspects of the MIMO UWB-IR Synchronizer

Conclusions

mimo uwb ir system model with poisson distributed multipath fading

SPACE-TIME CODED

PACKET TRANSMITTER

ADOPTING OPPM

MODULATION FORMAT

NON-COHERENT

ML

DECODER

MIMO UWB-IR System Model(with Poisson distributed multipath fading)

PILOT SIGNAL

GENERATOR

FOR

SYNCHRONISM

RECOVERY

NON-COHERENT

ML

SYNCHRONIZER

the mimo uwb ir channel model
The MIMO UWB-IR channel model

Multiple Cluster SISO channel responses with Poisson distributed arrivals and clusters and Log-Normally distributed path gains. ( It has been adopted for describing different indoor and outdoor propagation environments)

A. Molish, D. Cassioli, et alii, “A Comprehensive Standardized Models for UltraWideband Propagation Channels”, IEEE Tr. On antennas and Propagation, Vol.54, No.11, pp.3151-3166, Nov.2006.

main assumptions on the channel model
Main assumptions on the channel model

A.1) According to

J.H.Reed, An introduction to Ultra Wideband Communication Systems, Prentice Hall 2005

we may approximate each Multiple Cluster SISO channel response to single cluster one, by considering only the first cluster.

A.2) In order to derive the co-decoder block we consider three different path gains’ ddp:

1) Gaussian

2) Log-Normal

3) Nakagami

A.3) In order to derive the co-decoder block we assume the number V of arrivals and their values to be perfectly estimated

A.4) The path gains are supposed to be spatially uncorrelated

A.5) We consider slow-variant fading

ml decoder block scheme
ML Decoder Block Scheme

NON-COHERENT

ML

SYNCHRONIZER

Banks of Filters

matched to

M-OPPM symbols

and their V+1 replicas

.

.

.

Decision

Statistics

Processing

and selector

of maximum

setting of the pulse width t p to mitigate the inter pulse interference ipi
Setting of the pulse width TP to mitigate theInter-Pulse-Interference (IPI)

Given the following positions :

a) , temporal pulse width (monocycle) used by each transmit antennas

b) M, the OPPM constellation cardinality of the symbols used for Space-Time coding of the L-ary Source Symbols.

c) , the exponentially distributed inter-arrivals with arrival mean frequency equal to

Let us set , to meet the following condition:

for a fraction h of the service time, that is

Such choice allows us to mitigate the IPI effect due to the Poisson distributed arrivals

the outputs of matched filters matrix representation

stands for the (NtX (Nr (V+1)) ) multipath channel matrix

The outputs of matched filters (matrix representation)

stands for unitary (MxNt ) Space-Time codeword matrix corresponding to the M-OPPM coded symbols, that is

denotes Unitary (MX1) vector. It is function of the uncoded L-ary source symbol “l”, and biunivocally associated to the M-ary OPPM coded symbol radiated by the i-th transmit antenna

stands for (MxNr (V+1 ) ) Additive Gaussian noise matrix

is the signal to noise ratio per each transmitted bit

Nfis the number of frame per each symbol period Ts

decision statistics processing and selector of maximum
Decision Statistics processing and selector of maximum
  • The ML Decoder works according to the following criterium:
s pace t ime o rthogonal p ulse p osition m odulation stoppm codes
Space Time Orthogonal Pulse Position Modulation (STOPPM) codes

Definition

1) The unitary codeword matrices are composed by M rows and Nt columns. The number M (that is, the OPPM constellation cardinality) is given by product LNt

2) Any two distinctive codeword matrices

are composed by 2Nt different columns

Property of the STOPPM codes

The spectral efficiency of the STOPPM codes is equal to

Es: L=Nt=2

M=4

the union chenoff upper bound retained stoppm codes
The Union-Chenoff upper bound retained STOPPM codes
  • “Log-Normal” frustraction integral. It cannot be expressed in closed form .
  • S.M.Hass, J.H.Shapiro, “Space-Time Codes for Wireless Optical Communications”, Eurasip Journal on Applied Signal Processing, pp. 211-220, no.3, 2002.
performance of the stoppm codes
Performance of the STOPPM codes

Nk- fading

G-fading

  • Nr=3
  • Nf=6

Lg-N fading

CM3’s

Multipath Intense Profile

coverage ranges and troughput 1 2
Coverage Ranges and Troughput(1/2)
  • BER target:
  • Transmit Power: 2.5mW (Typically adopted for outdoor systems)
  • Each parameter of SISO links is according to CM1:
  • 4) The baseband monocycle is equal to the Gaussian pulse second derivative
  • M.Z.Win, R.A.Scholtz, ''Ultra-Wide Banbwidth Time-Hopping Spread Spectrum
  • Impulse Radio for Wireless Multiple Access Communications'', IEEE Tr. on Comm.,
  • vol.48, pp.679-691, Apr.2002.
  • 5) The path loss model is according to the Siviak-Petroff one
  • K.Siwiak, A.Petroff, ''A Path link model for Ultra Wide Band
  • Pulse Transmissions'', IEEE VTC2001, Rhodes, Greek, May 2001.
  • 6) Throughput: 136.0Mbps
  • 7) The Log-Normal fading is considered
coverage ranges and troughput 2 2
Coverage Ranges and Troughput(2/2)

Table of coverage Ranges reached by the proposed MIMO UWB-IR co-decoder , equipped with the STOPPM codes. Any SISO link is according to CM1.

the ipi effect
The IPI effect

CM3’s Multipath Intense Profile

G fading Nt=2, Nr=1, Nf=4

slide18

Channel Impairments – Spatially correllated Fading (1/2)

A.Paulray, R.Nabar, D.Gore, Introduction to Space-Time

Wireless Communications, Cambridge university Press, 2003.

Spatial Covariance Matrix.

slide19

Channel Impariments- Spatially Correlated Fading (2/2)

Lg-N fading

Nt=Nr=2, Nf=12

CM3’s Multipath Intense Profile

channel impairments cross polarization
Channel Impairments- Cross-Polarization

A.Paulray, R.Nabar, D.Gore, Introduction to Space-Time

Wireless Communications, Cambridge university Press, 2003.

Channel Model

Nakagami Fading Nt=Nr=2, Nf=15

CM3’s Multipath Intense Profile

snr losses due to asynchronism
SNR losses due to Asynchronism
  • Let us assume that any time arrival estimate is affected by some error , that is
mimo uwb ir system model with poisson distributed multipath fading1

SPACE-TIME CODED

PACKET TRANSMITTER

ADOPTING OPPM

MODULATION FORMAT

NON-COHERENT

ML

DECODER

MIMO UWB-IR System Model(with Poisson distributed multipath fading)

PILOT SIGNAL

GENERATOR

FOR

SYNCHRONISM

RECOVERY

NON-COHERENT

ML

SYNCHRONIZER

slide24

NON Coherent ML Synchronizer- Main Aspects (1/2)

  • It jointly estimates the number V of arrivals and their values , according to the ML criterium, without any knowledge on the magnitude of the channel coefficients
  • Such estimation is asymptotically exact
  • It is pilot-aided
  • From Cramer-Rao bound point of view, the SIMO version is to prefer to a MIMO version with orthogonal signaling
  • E.Baccarelli, M.Biagi, C.Pelizzoni, N.Cordeschi, “Multi-Antenna Noncoherent ML Synchronization for UWB-IR faded channels ”, Journal of Communications and Networks (JCN), vol. 8, No.2, pp.194-204, Giugno 2006
joint ml estimation of v and
Joint ML estimation of V and

Prop.1:

Let us indicate the arrival times’ and channel coefficients vectors, and let be a received signal G.S. representation, then the following joint ML estimation

can be equivalently effected by only estimanting the arrivals times and their number V, that is

with

the ml equations system
The ML equations’ system

Properties of the resulting ML equation system :

  • The i-th equation is function only on the corespondent time arrival. The (V+1) equations are independent each other
  • Any solution can be admitted only when :

Serial implementation

slide28

ML Synchronizer

(Early-Late Gate serial version)

yNr(t)

LNr

“late”output

X

dt

blocco Lj

+

y1(t)

yj(t)

L1

X

(1)

dt

Tw

Late 

X

Tw

(2)

-

Template Signal

Generator

LOOP FILTER

+

+

Early 

(1+Ns)

Tw

E1

+

“early”output

ENr

+

conclusions
Conclusions
  • The proposed MIMO UWB-IR co-decoder is optimized to work under different path gains pdfs
  • It works in non-coherent mode
  • The proposed STOPPM codes can minimize the Union-Chernoff upper bounds
  • The resulting solution allows to extend the (typically) low coverage of the SISO UWB-IR systems
  • The proposed ML synchronizer can be simply implemented as serial version of early-late gate.