Communications and Networking Part 6 docx

JPEG 2000, the newest image representation standard, addresses this issue firstly by including predefined error resilient tools in his core encoding system part 1 and going straightforwa

MC-CDMA Systems: a General Framework for Performance Evaluation with Linear Equalization 139

Fig 4 The impact of the parameter β on the BEP as a function of the number of users for

M = 1024 and γ = 10 dB

In Fig 4 the impact of different equalization strategies on the BEP as a function of the

number of active users, Nu, is reported for γ = 10 dB and M = 1024 First of all it can be

noted that the optimum β always provides the better performance; then, it can be observed that when few users are active MRC represents a good solution, approaching the optimum,

crossing the performance of EGC for a system load about 1/64 ÷ 1/32 (i.e., Nu = 16 ÷ 32) and the performance of a TORC detector with ρTH = 0.25 for a system load about 1/16 ÷ 1/8 Note that a fixed value of β equal to 0.5 represents a solution close to the optimum for

system loads ranging in 1/4 ÷ 1 (i.e., Nu = 256 ÷ 1024) and the performance still remain in the same order for all system loads

7 Combined equalization

Another approach to combine the sub-carriers contributions consists in applying equalization at the transmitter in conjunction with post-equalization at the receiver, thereby splitting the overall equalization process on the two sides (Masini & Conti, 2009) We will call this process combined equalization (CE) The transmitter and receiver block schemes are depicted in Fig 5

pre-A similar approach was proposed in (Cosovic & Kaiser, 2007), where the performance was analytically derived in the downlink for a single user case and in (Masini, 2008), where PE was considered at the transmitter and threshold ORC (TORC) at the receiver For time division duplex direct sequence-CDMA systems a pre and post Rake receiver scheme was presented in (Barreto & Fettweis, 2000) Here we present a complete framework useful to evaluate the performance of CE (i) in a multiuser scenario; (ii) analytically evaluating optimal values for PE parameters; (iii) investigating when combined equalization introduces some benefits with respect to classical single side equalization techniques

(a) Transmitter block scheme (ϕm = 2π f m t + φm , m = 0 .M– 1 )

(b) Receiver block scheme (ϕm = 2π f m t + ϑm , m = 0 .M– 1)

Fig 5 Transmitter and receiver block schemes in case of combined equalization

We assume CSI simultaneously available at both the transmitter and the receiver in order to

evaluate the impact of a combined equalization at both sides on the system performance in

terms of BEP with respect to single-side equalization In particular we assume PE performed

at both sides, thus allowing the derivation of a very general analytical framework for the

BEP evaluation and for the explicit derivation of the performance sensitivity to the system

MC-CDMA Systems: a General Framework for Performance Evaluation with Linear Equalization 141

0 pre

m m M

m i

m m m

H G

with βT representing the PE coefficient at the transmitter

The coefficient G m,pre has to be normalized such that the transmit power is the same as in the

case without pre-equalization, that means

,pre 0

M m m

Note that when βT = –1, 0, and 1, coefficient in (41) reduces to the case of MRC, EGC and

ORC, respectively Since we are considering the downlink we assume perfect phase

compensation, the argument of G m,pre can be included inside φm in (40), explicitly considering

only its absolute value

Note that, to perform pre-equalization, CSI has to be available at the transmitter; this could

be possible, for example, in cellular systems where the mobile unit transmits pilot symbols

in the uplink which are used by the base station for channel estimation

At the receiver side, the post-equalization coefficient has to take into account not only the

effect of channel but also of pre-equalization in order to counteract additional distortion

caused by the last one (see Fig 5) Hence, it is given by

where βR is the post-equalization parameter Note again that when βR = –1, 0 and 1, (45)

reduces to MRC, EGC and ORC, respectively

8 Decision variable for combined equalization

Adopting the same procedure as in Sec 4 and, hence, by linearly combining the weighted

signals from each sub-carriers, we obtain the decision variable

po

1

( ) (

st )

, 0

M

n n

l l l

=

where the received signal before combination can be evaluated as

T

T

u T

T

1 20

l

k k n i

0

i i l l

where U, I, and N represent the useful, interference, and noise term, respectively and whose

statistic distribution has to be derived to evaluate the BEP

Following the same procedure adopted in Sec 4, we obtain

Also in this case, since a (k) is zero mean and statistically independent of αl and n l , and

considering that n l and αl are statistically independent and zero mean too, then E{IN} = E{IU}

= 0 Since n l and αl are statistically independent, then E{NU} = 0 Moreover I, N, and U are

uncorrelated Gaussian r.v.’s, thus also statistically independent

9 Bit error probability evaluation with combined equalization

By applying the LLN to the useful term, that is by approximating U with its mean value, the

BEP averaged over small-scale fading results

2 f

MC-CDMA Systems: a General Framework for Performance Evaluation with Linear Equalization 143

where Ξ is the signal-to-noise plus interference-ratio (SNIR) given by

Note that when one between βT or βR is zero, (53) reduces to (34)

10 Optimum combination with combined equalization

We aim at deriving the optimal choice of the PE parameters, thus the couple (βT, βR) jointly

minimizing the BEP

However, being in the downlink, the receiver is in the mobile unit, hence, it is typically more

convenient, if necessary, to optimize the combination at the transmitter (i.e., at the base

station), once fixed the receiver Therefore, we find the optimum values of βT defined as that

values within the range [–1,1] that minimizes the BEP for each βR

By deriving (54) with respect to βT and after some mathematical manipulation, we obtain the

implicit solution given by (15)

11 Numerical results for combined equalization

In Fig 6, the BEP is plotted as a function of βT for different values of βR and mean SNR

γ = 10 dB in fully loaded system conditions (M = Nu = 1024) Note that, in spite of the post-

PE technique, there is always an optimum value of βT minimizing the BEP and this value

depends on βR Moreover, the BEP is also drastically dependent on βR, meaning that a not

suitable post-PE technique can even deteriorate the performance, with respect to one side

combination, rather than improving it Simulation results are also reported confirming the

analysis especially in correspondence to the optimal βR (note that the analysis is confirmed

for 64 sub-carriers and thus it is expected to be even more accurate for higher number of

sub-carriers).5

5 Similar considerations can be drawn for time- and -frequency correlated SUI-x channels as shown, by

simulation, in (Masini et al., 2008) referred to PE at the receiver

13, Issue 12, December 2009 Page(s):884 – 886 ©2009 IEEE

In Fig 7, the BEP is plotted as a function of the mean SNR, γ , in fully loaded system

conditions (M = Nu = 1024) The effect of the combining techniques at the transmitter and the receiver can be observed: a suitable choice of coefficients (such as βT = 0.5 and βR = 0.5) improves the performance with respect to single side combination (βT = 0, βR = 0.5); however, a wrong choice (such as βT = 0.5 and βR = –1) can drastically deteriorate the BEP

In Fig 8, the BEP as a function of the system load SL in percentage is shown for γ = 10 dB and different couples (βT, βR) Note how a suitable choice of pre- and post-PE parameters can increase the sustainable system load At instance, by fixing a target BEP equal to 4 · 10–3, with combination at the transmitter only (i.e., βT = 0.5, βR = 0) we can serve the 45% of users, while fixing βT = 0.5 and adaptively changing βR following the system variations (i.e., always setting βR at the optimum value minimizing the BEP), the 100% of users can be served The same performance can be obtained by fixing the combination parameter at 0.5 at the transmitter or at the receiver and adaptively changing the combination parameter at the

MC-CDMA Systems: a General Framework for Performance Evaluation with Linear Equalization 145

12 Final considerations

We summarized the main characteristics of MC-CDMA systems and presented a general framework for the analytical performance evaluation of the downlink of MC-CDMA systems with PE

We can conclude that MC-CDMA systems may be considered for next generation mobile radio systems for their high spectral efficiency and the low receiver complexity due to the avoidance of ISI and ICI in the detection process The spreading code length can be dynamically changed and not necessarily equal to the number of sub-carriers enabling a flexible system design and further reducing the receiver complexity

βT =0.5, βR =0.5

βT =0.5, βR (opt)

= - 0.5, = 0.5

Fig 8 BEP vs the system load SL for various βT and βR when γ = 10 dB Figure reprinted

with permission from B M Masini, A Conti, “Combined Partial Equalization for MC-CDMA Wireless Systems”, IEEE Communications Letters, Volume 13, Issue 12, December 2009

Page(s):884 – 886 ©2009 IEEE

To enhance their performance, PE can be adopted in the downlink, allowing good performance in fading channels still maintaining low the receiver complexity

The optimal choice of the PE parameter is fundamental to improve the performance in terms

of BEP averaged over small-scale fading

When CE is adopted at both the transmitter and the receiver a proper choice of PE parameters is still more important, to significatively improve the performance with respect

to single-side detection

The gain achieved by a suitable combination of transmission and reception equalization parameters could be exploited to save energy or increase the coverage range (a similar approach was used for partial power control in cellular systems in (Chiani et al., 2001))

In case of non-ideal channel estimation, the performance results to be deteriorated; however,

it has been shown that the optimum PE parameter is not significatively affected by channel estimation errors The analysis for correlated fading channels and imperfect CSI has been

MC-CDMA Systems: a General Framework for Performance Evaluation with Linear Equalization 147 performed in (Zabini et al., to appear) optimum PE parameter with perfect CSI This means that, in practical systems, it is possible to adopt the value of the PE parameter which would

be optimum in ideal conditions (it is simple to evaluate and does not require the knowledge

of the channel estimation error) without a significant loss of performance, even for estimation errors bigger than 1% (Zabini et al., 2007; to appear)

The effect of block fading channels and time and frequency correlated fading channel on the performance of MC-CDMA systems with PE has been investigated in (Masini & Zabini, 2009) and (Masini et al., 2008), respectively, still showing the goodness of PE as linear equalization technique and still demonstrating that the PE parameter that is optimum in ideal scenarios still represents the best choice also in more realistic conditions

13 References

Barreto, A & Fettweis, G (2000) Performance improvement in ds-spread spectrum cdma

systems using a pre- and a post-rake, Zurich, pp 39–46

Chiani, M., Conti, A & Verdone, R (2001) Partial compensation signal-level-based up-link

power control to extend terminal battery duration, Vehicular Technology, IEEE Transactions on 50(4): 1125 –1131

Conti, A., Masini, B., Zabini, F & Andrisano, O (2007) On the down-link performance of

multi-carrier CDMA systems with partial equalization, IEEE Transactions on Wireless Communications 6(1): 230–239

Cosovic, I & Kaiser, S (2007) A unified analysis of diversity exploitation in multicarrier

cdma, IEEE Transactions on Vehicular Technology 56(4): 2051–2062

Gradshteyn, I & Ryzhik, I (2000) Table of Integrals, Series and Products, Academic Press Hanzo, L & Keller, T (2006) OFDM and MC-CDMA - A Primer, J Wiley & Sons ISBN:

0470030070

Hanzo, L., Yang, L.-L., Kuan, E.-L & Yen, K (2003) Single and Multi-Carrier DS-CDMA:

Multi-User Detection, Space-Time Spreading, Synchronization and Standards, J.Wiley &

Sons

K Fazel, S K (2003) Multi-Carrier and Spread Spectrum Systems, Wiley

Masini, B (2008) The impact of combined equalization on the performance of mc-cdma

systems, Journal of Communications 3(5): 2051–2062

Masini, B & Conti, A (2009) Combined partial equalization for MC-CDMA wireless

systems, IEEE Communications Letters 13(12): 884–886

Masini, B., Leonardi, G., Conti, A., Pasolini, G., Bazzi, A., Dardari, D & Andrisano, O

(2008) How equalization techniques affect the tcp performance of mc-cdma

systems in correlated fading channels, EURASIP Journal on Wireless Communications and Networking (Article ID 286351)

Masini, B & Zabini, F (2009) On the effect of combined equalization for mc-cdma systems

in correlated fading channels, IEEE Wireless Communications and Networking Conference, WCNC, pp 1 –6

Slimane, S (2000) Partial equalization of multi-carrier cdma in frequency selective fading

channels, New Orleans, USA, pp 26–30

Yee, N., Linnartz, J.-P & Fettweis, G (1993) Multi-Carrier-CDMA in indoor wireless

networks, Proceedings of Personal, Indoor and Mobile Radio Conference, PIMRC,

Yokohama, pp 109–113

Zabini, F., Masini, B & Conti, A (2007) On the performance of MC-CDMA systems with

partial equalization in the presence of channel estimation errors, 6th IEEE International Workshop on Multi Carrier Spread Spectrum (MC-SS), Herrsching,

Germany, pp 407– 416

Zabini, F., Masini, B., Conti, A & Hanzo, L (to appear) Partial equalization for MC-CDMA

systems in non-ideally estimated correlated fading, IEEE Transactions on Vehicular Technology

7

Wireless Multimedia Communications and

Networking Based on JPEG 2000

Max AGUEH

ECE Paris France

1 Introduction

Nowadays, more and more multimedia applications integrate wireless transmission functionalities Wireless networks are suitable for those types of applications, due to their ease of deployment and because they yield tremendous advantages in terms of mobility of User Equipment (UE) However, wireless networks are subject to a high level of transmission errors because they rely on radio waves whose characteristics are highly dependent of the transmission environment

In wireless video transmission applications like the one considered in this chapter and presented in Figure 1, effective data protection is a crucial issue

JPEG 2000, the newest image representation standard, addresses this issue firstly by including predefined error resilient tools in his core encoding system (part 1) and going straightforward by defining in its 11th part called wireless JPEG 2000 ( JPWL) a set of error resilient techniques to improve the transmission of JPEG 2000 codestreams over error-prone wireless channel

Fig 1 Wireless video streaming system

camcorder

Video server

Wireless Client

Encoder JPWL

Decoder JPWL

Its main characteristics are: lossy or lossless compression modes; resolution, quality and spatial scalability; transmission and progressive image reconstruction; error resilience for low bit rate mobile applications; Region Of Interest (ROI) functionality, etc

Part 1 of the standard defines different tools allowing the decoder to detect errors in the transmitted codestream, to select the erroneous part of the code and to synchronise the decoder in order to avoid decoder crash Even if those tools give a certain level of protection from transmission errors, they become ineffective when the transmission channel experiment high bit error rate Wireless JPEG 2000 (JPEG 2000 11th part) addressed this issue

by defining techniques to make JPEG 2000 codestream more resilient to transmissions errors

2000 codestreams interleaving is not considered in (Nicholson et al, 2003)

In this chapter we address the problem of robust and efficient JPEG 2000 images and video transmission over wireless networks The chapter is organized as follows: In section 2, we present a state of art of wireless JPEG 2000 multimedia communication systems along with the challenges to overcome in terms of codestreams protection against transmission errors

In section 3, we provide an overview of channel coding techniques for efficient JPEG 2000 based multimedia networking Finally section 4, provides discussions and prospective issues for future distribution of motion JPEG 2000 images and video over wireless networks

2 Wireless JPEG 2000 multimedia communication system and its challenges

In high error rate environments such as wireless channels, data protection is mandatory for efficient transmission of images and video In this context, Wireless JPEG 2000 (JPWL) the

11th part of JPEG 2000 (JPWL, 2005) different techniques such as data interleaving, Forward Error Correction (FEC) with Reed-Solomon (RS) codes etc in order to enhance the protection of JPEG 2000 codestreams against transmission errors

In wireless multimedia system such as the one considered in this chapter (see Figure 1), a straightforward FEC methodology is applying FEC uniformly over the entire stream (Equal Error Correction - EEP) However, for hierarchical codes such as JPEG 2000, Unequal Error Protection (UEP) which assigns different FEC to different portion of codestream has been considered as a suitable protection scheme

Since wireless channels' characteristics depend on the transmission environment, the packet loss rate in the system also changes dynamically Thus a priori FEC rate allocation schemes such as the one proposed in (Agueh et al, 2007, a) are less efficient Two families of data protection schemes address this issue by taking the wireless channel characteristics into

Wireless Multimedia Communications and Networking Based on JPEG 2000 151 account in order to dynamically assign the FEC rate for JPEG 2000 based images/video The first family is based on a dynamic layer-oriented unequal error protection methodology whereas the second relies on a dynamic packet-oriented unequal error protection methodology Hence, in the first case, powerful RS codes are assigned to most important layers and less robust codes are used for the protection of less important layers It is worth noting that in this case, all the JPEG 2000 packets belonging to the same layer are protected with the same selected RS code Examples of layer-oriented FEC rate allocation schemes are available in (Guo et al, 2006) and (Agueh et al, 2007, b) On the other side, in packet-oriented FEC rate allocation schemes such as the one presented in (Agueh et al, 2008), RS codes are assigned by decreasing order of packets importance In (Agueh et al, 2008), we demonstrate that the proposed optimal packet-oriented FEC rate allocation is more efficient than the layer-oriented FEC rate allocation scheme presented in (Guo et al, 2006) and (Agueh et al,

2007, b) However, layer-based FEC rate allocation schemes have low complexity while packet-oriented FEC allocation methodologies are complex especially when the number of packets in the codestream is high In this case, packet oriented FEC schemes are unpractical for highly time-constrained images/video streaming applications In this case switching to a layer oriented FEC rate allocation scheme is more interesting The smart FEC rate allocation scheme proposed in (Agueh et al, 2009, a) address this issue by allowing switching from a packet oriented FEC scheme to a layer oriented scheme such as the ones proposed in (Agueh

et al, 2009, b)

In section 2.1 we present the packet oriented system proposed in (Agueh et al, 2008) to address the issue of robust JPEG 2000 images and video transmission over wireless network Then in section 2.2 the layer-oriented scheme proposed in (Agueh et al, 2009, b) is described Finally, in section 2.3 we present the system proposed in (Agueh et al, 2009, a) to unify packet and layer based scheme

2.1 Optimal Packet-oriented FEC rate allocation scheme for robust Wireless JPEG

2000 based multimedia transmission

The functionalities of the proposed JPWL packet-oriented system are presented in Figure 2 The aim of this system is to efficiently transmit a Motion JPEG 2000 (MJ2) video sequence through MANET channel traces

The system is described as follows:

The input of the JPWL codec is a Motion JPEG 2000 (MJ2) file The JPEG 2000 codestreams included in the MJ2 file are extracted and indexed

These indexed codestreams are transmitted to the JPWL encoder (JPWL, 2005) presents a more accurate description of the used JPWL encoder) which applies FEC at the specified rate and adds the JPWL markers in order to make the codestream compliant to Wireless JPEG

2000 standard At this stage, frames are still JPEG 2000 part 1 compliant, which means that any JPEG 2000 decoder is able to decode them

To increase JPWL frames robustness, an interleaving mechanism is processed before each frame transmission through the error-prone channel This is a recommended mechanism for transmission over wireless channel where errors occur in burst (contiguous long sequence of errors) Thanks to interleaving the correlation between error sequences is reduced

The interleaving step is followed by RTP packetization In this process, JPEG 2000 codestream data and other types of data are integrated into RTP packets as described in (Schulzrinne et al, 2003)

Fig 2 JPWL based system functionalities

RTP packets are then transmitted through the wireless channel which is modelled in this work by a Gilbert channel model At the decoder side, after depacketization, the JPWL decoder corrects and decodes the received JPWL codestreams and rebuilds the JPEG 2000

frames At this stage, parameters such as Packet Error Rate ( PER ) are extracted, increasing

the knowledge of the channel state The decoder sends extracted parameters back to the JPWL encoder via the Up link The last process of the transmission chain is the comparison between the transmitted and the decoded image/video Figure 3 presents JPEG 2000 codestreams transmission through the JPWL packet-oriented FEC system

Wireless Multimedia Communications and Networking Based on JPEG 2000 153

2.2 Optimal Layer-oriented FEC rate allocation scheme for robust Wireless JPEG 2000 based multimedia transmission

Unlike the system described in (Agueh et al, 2008), where the FEC rate allocation scheme is packet oriented, in the current system we consider a layer oriented FEC rate allocation scheme In other words the difference between both systems is the FEC rate allocation module Actually, in the packet oriented scheme the redundancy is added by taking the packets importance into account (see Figure 3) while in the layer oriented scheme we rely on layers importance to allocate the adequate RS codes (see Figure 4)

Fig 4 A JPEG 2000 codestreams transmission through the JPWL layer-oriented FEC system

2.3 Smart combined Packet/layer based FEC rate allocation scheme for robust

Wireless JPEG 2000 based multimedia transmission

The functionalities of the proposed smart JPWL based system are presented in Figure 5

In this system, indexed JPEG 2000 codestreams are transmitted to the smart FEC rate allocation module If the number of data packets available in the codestreams is low (typically under the defined smart threshold), the smart module uses the optimal packet-oriented FEC rate allocation methodology presented in (Agueh et al, 2008) whereas it switches to the dynamic layer-oriented FEC rate allocation methodology presented in (Agueh et al, 2009, b) when the number of data packets is high Ones the protection rate determined, the codestreams are transmitted to the JPWL encoder which applies FEC at the specified rate and adds the JPWL markers in order to make the codestream compliant to Wireless JPEG 2000 standard Hence, Figures 3 and 4 correspond to the JPWL protection where redundant data are added to original codestreams If the JPEG 2000 Frame which is

being processed is constituted by less than a defined threshold (smart_thresh) , then the

smart FEC rate allocation scheme emulates a scenario similar to the one presented in Figure

3 (packet-oriented FEC rate allocation) Otherwise, it emulates the scenario of Figure 4 (dynamic layer-oriented FEC rate allocation) Protected data are then interleaved and the interleaved codestreams go through the other processes described in section 2.1

Original codestreams

Layer-Oriented JPWL Protection

Protection