Future Transmitter/Receiver Diversity Schemes in Broadcast Wireless Networks

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CORE ACCEPTED FROM OPEN CALL Metadata, citation and similar papers at core.ac.uk Provided by Brunel University Research Archive Future Transmitter/Receiver Diversity Schemes in Broadcast Wireless Networks

Yue Zhang, John Cosmas, and YongHua Song, Brunel University Maurice Bard, Broadreach Systems

ABSTRACT well documented technique where each pair of transmit and receive antennas provides a differ- An open diversity architecture for a cooperat- ent signal path from the transmitter to the ing broadcast wireless network is presented that receiver. By sending signals that carry the same exploits the strengths of the existing digital information through these different paths, multi- broadcast standards. Different diversity tech- ple independently faded replicas of the data niques for broadcast networks that will minimize symbol can be obtained at the receive end. Max- the complexity of broadcast systems and improve imum diversity gain is achieved when fading is received SNR of broadcast signals are described. uncorrelated across antenna pairs. Resulting digital broadcast networks could More recent work has focused on investigat- require fewer transmitter sites and thus be more ing how techniques such as trellis-based space- cost effective with less environmental impact. time codes [4, 5] and orthogonal designs [6] can Transmit diversity is particularly investigated be applied to multiple transmit antennas to max- since it obviates the major disadvantage of imize the diversity gain. Unfortunately, space- receive diversity being the difficulty of locating time coding is not compliant with current two receive antennas far enough apart in a small standards for broadcast systems; therefore, only mobile device. The schemes examined here are spatial diversity techniques can be applied. If compatible with existing broadcast and cellular multiple signals are received with short delay telecom standards, and can be incorporated into spread, the OFDM signal is faded equally across existing systems without change. the channel in a flat fade; this induces long error bursts that are hard to correct since there is INTRODUCTION insufficient frequency selectivity to be exploited by the coding and interleaving schemes. Cyclic The vision for future mobile communications delay diversity (CDD) [7] is a very simple and networks is of an open architecture supporting elegant method that, when combined with a multiplicity of international standard wire- MIMO, improves frequency selectivity, thereby less network technologies ranging from sec- randomizing the channel response. The compu- ond-/third-/fourth-generation (2G/3G/4G) tational cost of CDD is very low, as all signal cellular radio systems (GSM, GPRS, UMTS) processing needed is performed on the OFDM to wireless local area networks (WLANs), signals in the time domain. broadband radio access networks (BRANs) to This article focuses on an open wireless diver- digital video and audio broadcast networks sity structure. First, we introduce the system (DVB, DAB) [1]. model and then discuss different diversity tech- Future mobile radio systems are expected to niques, including CDD for transmitter and maxi- deliver services, which inherently require high mum ratio combining (MRC) for receiver. The data rates. Orthogonal frequency-division multi- application of CDD to DVB-H systems is dis- plexing (OFDM) [2] is an ideal technique for cussed, and results of simulations are presented. broadband transmission in multipath fading Finally, we present the conclusions of this study. environments and is implemented in broadcast standards like DAB or DVB as well as WLAN SYSTEM MODEL standards [3] such as HIPERLAN/2 or IEEE 802.11a/g and WiMAX. Spatial diversity can be OFDM used to improve the error performance and OFDM is a proven technique for achieving high channel capacity in these systems by overcoming data rates and overcoming multipath fading in degradations caused by scattering environments. wireless communication. OFDM can be thought The use of multiple transmit and receive anten- of as a hybrid of multicarrier modulation (MCM) nas (multiple-input multiple-out, MIMO) is a and frequency shift keying (FSK) modulation.

Transmitter The block interleaver can be described as Outer Inner QAM Data source Outer coder Inner coder interleaver interleaver mapping a matrix to which data is written in Pilot and TPS columns and read in OFDM signals modulator rows. The modulator

MIMO channel NxM MIMO Frame process is equivalent encoder adaptation to an inverse OFDM discrete Fourier modulator transform, while the demodulation Channel equalization process is equivalent OFDM to a discrete Fourier Synchronization demodulation transform. MIMO decoder OFDM Synchronization demodulation

Channel estimator

Received Outer Outer Inner Inner QAM data decoder deinterleaver decoder deinterleaver demodulation

Receiver

MIMO scheme added Required part for DVB-H to DVB-H transmission systems

I Figure 1. End-to-end MIMO system diagram of DVB-T/H transmission with coded data.

Orthogonality among carriers is achieved by sep- coder is Reed-Solomon shortened code arating them by an integer multiple of the RS(204,188) derived from the original systematic inverse of symbol duration of the parallel bit- RS(255,239) code. The inner coder comprises a streams, thus minimizing intersymbol interfer- puncture coder and a convolutional coder. The ence (ISI). Carriers are spread across the puncture coder is based on the mother convolu- complete channel, fully occupying it and hence tional code of rate 1/2 with 64 states. The convo- using the bandwidth very efficiently. The OFDM lutional coder increases error correction receiver uses adaptive bit loading techniques capability and codes used are similar to those based on a dynamic estimate of the channel widely employed in digital communication sys- response, to adapt its processing and compen- tems such as GSM, IS95, and WLAN systems: sate for channel propagation characteristics and convolutional code generators of x6 + x4 + x3 + achieve near ideal capacity. This most important x + 1 and x6 + x5 + x4 + x3 + 1. A puncture advantage of OFDM systems over single-carrier coder is a common solution employed to reduce systems is obtained when there is frequency- the loss of data throughput capacity caused by a selective fading. The signal processing in the convolutional coder. This is done by not trans- receiver is rather simple; distortion of the signals mitting some of the bits output by the convolu- is compensated by multiplying each subcarrier by tional coder, but results in the receiver having to a complex transfer factor, thereby equalizing the implement different convolution puncture channel response. It is not feasible for conven- decoders for each of the puncture patterns used. tional single-carrier transmission systems to use An inner interleaver is used to distribute trans- this method. mitter bits in time or frequency or both to However, some disadvantages of OFDM sys- achieve an optimum distribution of bit errors tems are that the peak-to-average power ratio after modulation. The block interleaver can be (PAPR) of OFDM is higher than for a single- described as a matrix to which data is written in carrier system, and OFDM is sensitive to a flat columns and read in rows. The modulator pro- fading channel. cess is equivalent to an inverse discrete Fourier OFDM is employed in the DVB-T and DVB- transform (IDFT), while the demodulation pro- H systems; a block diagram of a coded OFDM cess is equivalent to a discrete Fourier transform system for DVB-H is shown in Fig. 1. The outer (DFT).

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900 MHzm 50km/h, Max Doppler=41.67Hz, 100echos 11 2 5 E(r )=0.05 dB

0 22 -5 Transmitter Receiver -10

33dB

-15 M -20 Deep NM-25 fading 50 100 150 200 250 300 350 400 450 500 ms A B

900 MHzm 50km/h, Max Doppler=41.57Hz, 100echos 900 MHzm 30km/h, Max Doppler=25.00Hz, 100echos 5 35 E(r2)=0.60dB E(r2)=0.10dB 30 0

25 -5

20 -10 dB dB 15 -15 10 -20 5 2 0 E(r )=30.18 dB -25 50 100 150 200 250 300 350 400 450 500 100 200 300 400 500 ms ms C D

I Figure 2. a) M × N i.i.d MIMO channel; b) Rayleigh fading channel (E = 0.05 dB); c) Rician fading channel with Rician K-factor = 0.17 (E = 30.18 dB); and d) time histories of two uncorrelated MIMO channels (Rayleigh fading).

MIMO combined in such a way as to minimize the trans- A MIMO system utilizes multiple antennas at mission degradation that could be caused by per- the transmitter and receiver. Such systems have formance of each of the individual channels. demonstrated the ability to reliably provide high Effectiveness or “diversity gain” of an implemen- throughput in rich multipath environments. tation is dependent on the scenario for the prop- Spatial diversity employs the spatial proper- agation channels (e.g., rural or urban), ties of multipath channels, providing a new transmission data rate, Doppler spread, and dimension that can be exploited to enhance per- channel delay spread. formance. Coding and diversity are key elements In our modeling analysis we consider an of a successful MIMO implementation, while the equivalent baseband MIMO channel with N propagation channel and antenna installations transmit antennas and M receiver antennas have a major impact on system performance. illustrated in Fig. 2a. There are M × N channels Figure 1 also shows the additional compo- with independently distributed wide-sense sta- nents required for a typical coded MIMO sys- tionary uncorrelated scattered (WSSUS) tem. There are three kinds of MIMO techniques. Rayleigh-fading. If there is no direct line of The first aims to improve power efficiency by sight between the transmitter and the receiver, maximizing spatial diversity; such techniques the impulse response of the channel is modeled include delay diversity, space-time block codes by several paths, each with a Gaussian distribu- (STBC), and space-time trellis codes (STTC). tion of zero mean complex variable (envelope The second uses a layered approach to increase and phase), the envelope of which has a capacity (e.g., V-BLAST architecture), while the Rayleigh distribution shown in Fig. 2b. If we third exploits knowledge of the channel at the are modeling a transmission with direct line of transmitter. MIMO systems have proven to be sight between the transmitter and the receiver, very effective at combating time varying multi- then process does not have a zero mean, the path fading in broadband wireless channels. In envelope has a Rice distribution and the chan- these systems, replicas of the transmitted signal, nel is said to be a Rician fading channel, shown with uncorrelated variations in the time, fre- in Fig. 2c. The Rician K-factor is the ratio of quency, or spatial domain, or a combination of the power in the direct signal (fixed) to the all three arrive at the receiver. The replicas are total power received via indirect scattered

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paths. For fixed installations short-term ampli- with channel state information being tude variations in the received signal are gener- obtained from the training and pilot data. The disadvantage of ally caused by multipath reflections and •Diversity can be provided with multiple shadowing from moving objects. Mobile recep- transmit antennas combined with an appro- DD is that additional tion is generally non-line of sight (Rayleigh fad- priately designed channel code and inter- delays increase the ing), and signals are received indirectly from leaver pair. A disadvantage of this scheme total delay spread at reflections and refractions with an even greater is that the channel code leads to a loss in propensity for fading. Trees and road vehicles bandwidth efficiency. the receiver antenna, are major contributors but time variant multi- In our system we investigate DD schemes and an extension of path fading is also known to arise from bodies combined with the DVB channel code and inter- of water and buildings. Transmit diversity can leaver, which are categorized as a combination the guard interval improve non line of sight reception provided of the second and third choices in the above list. duration may be multiple signals are received with decorrelated required, reducing fading, and that the receiver can effectively DELAY DIVERSITY process the signals to its advantage. Diversity For delay diversity the same information is the bandwidth exploits the statistical nature of fading due to transmitted from both antennas simultaneous- efficiency of the multipath reducing the likelihood of deep fad- ly but with a delay of several symbol intervals. ing. Uncorrelated fading can be achieved The information signal is encoded by a chan- system. This through careful selection of spatial separation nel coder, and the output of the repetition disadvantage can be of the transmit antennas and by applying phase code is split into N parallel data streams, overcome by CDD. effects to the signals that help to decorrelate which are transmitted with a symbol delay them in the time domain. between them. Figure 3 shows an OFDM sys- As for the MIMO channel, there can be N tem with spatial transmit diversity applying transmit antennas and M receive antennas, and DD/CDD/PD/MRC. The cyclic extension is we assume that the MIMO channel is spatially the DVB guard interval and is inserted before separated sufficiently to ensure decorrelation of the delay shift, as shown in Fig. 3. UC means the multipath signals. The benefits of MIMO upconversion from the baseband into the radio diversity are realized when the fading on frequency (RF) band, and DC means down- received signals from the two channels are decor- conversion from the RF band to the baseband. related (i.e., they are fading independently), as δn denotes simple time shifts. To increase the shown in Fig. 2d. In this case it is much less like- frequency selectivity by multiple transmit ly that both signals are in a deep fade at the antennas, the delays of different antennas δn same time; therefore, a smaller fade margin can have to be chosen as k{n/B}. B is the band- be allowed for, and acceptable coverage can be width of the transmitted signal. predicted at a lower mean received signal k is a constant factor introduced for the sys- strength. tem design that has to be chosen large enough in order to guarantee a diversity gain; k = 2 is suf- PATIAL NTENNA IVERSITY ficient to achieve promising performance S A D improvements. To avoid ISI, the time delays plus This section describes the application of delay the multipath channel delay spread must be less diversity (DD), CDD, phase diversity (PD), and than the guard interval length. The disadvantage maximum ratio combining (MRC) to spatial of DD is that additional delays increase the total transmit/receive antenna diversity systems. These delay spread at the receiver antenna, and an diversity techniques can easily be applied to the extension of the guard interval duration may be existing DVB system standard with little effort required, reducing the bandwidth efficiency of and without impact on the standards. the system. This disadvantage can be overcome In general there are three ways of applying by CDD. transmit diversity; •Implicit or explicit channel information can CYCLIC DELAY DIVERSITY be fed back from the receiver to the trans- Figure 3 also shows the block diagram of an mitter to configure the transmitter, which OFDM system with CDD. The difference can switch the diversity parameters accord- between DD and CDD is the position of the ing to the information. In practice, howev- guard interval process. Figure 4 shows the differ- er, due to transmission time, vehicle ence between DD and CDD in the time domain. movements or dynamic interference can The cyclic extension is the guard interval for cause a mismatch between the channel each OFDM symbol. δcy is the delay for CDD, information as perceived by the transmitter and δ is the delay for DD (δcy = δ). τg is the and that perceived by the receiver. Up and guard time, and τmax is the channel maximum down transmission links are essential for delay spread (τg > τmax). The reference signal is this approach, so it is unsuitable for broad- undelayed and transmitted for both DD and cast networks. CDD. •Linear processing at the transmitter can The DD signal is a simple copy of the refer- spread the information across antennas; the ence signal, but, delayed by δ, ISI can be caused transmitter will send training data to the by the guard interval partly overlapping the sub- receiver for it to estimate the channel state sequent OFDM symbol in the reference signal at information, and this estimate is used to δ. In CDD there is no overlapping; the OFDM compensate for the channel response at the symbols for CDD can be generated from the ref- receiver. This capability can be exploited erence signal symbols just by applying a cyclic for DD, CDD, and PD in broadcast net- time shift δcy and subsequent insertion of the works since only a downlink is required, cyclic prefix. In this case the signal is not truly

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DVB-H is based on DVB-T and designed Guard- for mobile reception. OFDM interval UC It is a coded OFDM system containing an outer shortened ψ Guard- ej 1 OFDM δcy1 δ1 UC Reed-Solomon code interval concatenated with an inner (punctured) convolutional code.

For DVB-H three ψ Guard- ej N OFDM δcyN δN UC modules have been interval

added in the DVB-T OFDM transmitter wtih physical layer. DD/CDD/PD

Guard-interval OFDM Liner DC remove demodulator combine +

δ Guard-interval δcy OFDM jψ1 MRC MRC DC 1 remove 1 demodulator e

DC δ Guard-interval δcy OFDM ejψM M remove M demodulator

OFDM receiver with DD/CDD/PD/MRC

Only for PD Only for DD Only for CDD Only for MRC

Required part for all diversity schemes

I Figure 3. An OFDM system with CDD/DD/PD/MRC.

delayed between respective antennas but cycli- however, the BER is now not constant over the cally shifted; thus, there are no restrictions on subcarriers, and an outer forward error correc- the delay times, and there is no ISI. The impact tion (FEC) coder and decoder in conjunction of the receiver on DD and CDD schemes are with channel equalization can use the frequen- similar since the required signal processing is cy selectivity to its advantage by emphasizing performed in the time domain, and the DFT data on the strong subcarriers to overcome does not need to be duplicated for each receive data on the weak ones. antenna branch; thus, there is no increase in computational cost of the receiver. Moreover, it PHASE DIVERSITY is possible to apply CDD as a transmit diversity The application of phase diversity (PD) is also technique without knowing the channel informa- illustrated in Fig. 3, PD and CDD are processed tion at the transmitter. in a similar way by the receiver since a cyclic CDD has transformed the MIMO channel delay in the time domain corresponds to a fixed into a single-input multiple-output (SIMO) phase factor in the frequency domain. PD has to channel with increased frequency selectivity. be processed in the transmitter before OFDM The effect is illustrated in Fig. 5. In a flat fad- modulation and there is no resulting delay of the ing channel, where two signals of similar power signals at the transmit antennas. CDD and PD have been received with a half wavelength are independent of the guard interval and are delay, the bit error rate (BER) will be the able to increase the channel frequency selectivity same for each subcarrier, and CDD transforms without increasing the overall channel delay the flat fade into frequency selective fades. spread since these operations are computed The average BER for uncoded transmission before guard interval insertion and are restricted will be similar to that in a flat fading channel; to the OFDM symbol itself.

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RECEIVE DIVERSITY τ max Time section for The use of multiple antennas at the receiver, OFDM demodulation referred to as receive diversity, is exploited by Reference signal Cyclic OFDM-symbol using MRC. The signals from M receive anten- extension τ nas are combined linearly so as to maximize the δcy g ISI instantaneous SNR [9]. This is achieved by com- DD signal Cyclic -symbol bining the co-phased signals, making use of each extension OFDM of the receiver’s channel state information (CSI) δ δ to estimate the channel impulse response and compensate for channel effects including delay CDD signal Cyclic -symbol and phase. The SNR of the combined signal is extension OFDM equal to the sum of the SNR of all the branch δcy δcy signals. For an MRC system, illustrated in Fig. Time 3, the combining operations are performed at the subcarrier level after the DFT operation. I Figure 4. DD and CDD signals in time domain [7]. CE in Fig. 3 means channel estimation. The received OFDM signals at different antenna branches are first transformed via M separate –60 OFDM demodulator whose outputs are assigned Before CDD to N diversity combiners. In the MRC process each individual demodulated received signal is y (dB) –70 linearly combined, prior to equalization [7], the nsit MRC scheme effectively optimizes the SNR for de –80 each subcarrier. ctra

spe –90 er –100 APPLICATION TO THE Pow –5 –4 –3 –2 –1 0 1 2 3 45 6 DVB-H SYSTEM x10 –60 The above mentioned techniques can be applied After CDD

to broadcasting systems and still comply with the (dB)

DAB and DVB-T/H standards, in this section, sity –70

we examine application of CDD and MRC to den

the DVB-H system. ra –80

DVB-H is based on DVB-T and designed for pect

mobile reception. It is a coded OFDM system er s containing an outer shortened Reed-Solomon

Pow –90 (RS) code concatenated with an inner (punc- –5 –4 –3 –2 –1 0 1 2 3 45 6 tured) convolutional code. For DVB-H three f (Hz) x10 modules have been added in the DVB-T physical layer. One is 4k transmission mode, one is I Figure 5. Power spectra density of signals before CDD and after CDD UHF DVB-H transmission parameter signaling (TPS), (900mHz). and the other is in-depth interleavers. The 4k mode provides for 4096 carriers and has been added to the 2k and 8k modes of the DVB-T mitter, only a second signal path after the standard. The 4k mode brings additional flexibil- OFDM modulation has to be added. After ity in network design by providing better support channel coding (RS and Convolutional Cod- for SFNs and allowing high-speed reception. In ing) and interleaving, the bit-stream is mapped the DVB-T system the 2k transmission mode has to complex value QAM symbols. The “Frame been shown to provide better mobile reception Adaption” functional block is responsible for performance than 8k due to the larger intercarri- QAM symbol interleaving, pilot insertion and er spacing; however, the associated guard inter- transmission parameter signaling (TPS). The vals are very short due to the duration of the 2k resulting symbol stream is OFDM-modulated mode OFDM symbols. This makes the 2k mode split, up-converted and transmitted directly for only suitable for small SFNs, whereas the 4k one antenna and cyclically shifted for the OFDM symbol’s longer duration and longer other. The cyclic shift has to be added after guard interval makes it suitable for medium size modulation. SFN networks increasing the spectral efficiency An MRC receiver is implemented in the sim- for those networks. The symbol duration of 4k ulation model. After down-conversion, synchro- mode is shorter than the 8k mode enabling more nization and guard interval removal, the received frequent channel estimation computations in the OFDM signal is demodulated and equalized receiver, required for a rapidly changing channel using zero forcing, the model assumes perfect during mobile reception. 4k mode therefore pro- knowledge of the channel state information. vides a good trade-off between spectral efficien- Both complex valued symbol streams are com- cy for DVB-H network designers and high bined and QAM demodulated with soft-out val- mobility for DVB-H consumers. According to ues before symbol and bit-deinterleaving is [8], the parameters of 4k mode are shown in computed. Finally, the bit stream is soft-deci- Table 1. sion-maximum-likelihood (SDML) decoded in a In order to apply CDD at the DVB-H trans- Viterbi decoder.

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provide additional coding gain besides diver- Parameter 4k mode sity gain. In the case of an RA channel illustrated in Fig. 6b, TX diversity provides about Elementary period T 7/64 µs 9 dB gain in SNR at a BER of 2 × 10–4; this is much higher than the TU case since a TU Number of carriers 3409 channel has a maximum delay of 5 µs com- pared to the delay in an RA channel of 700 Value of carrier number Kmin 0 ns. Perfect knowledge of the CSI and synchronization has been assumed. Theoretical Value of carrier number Kmax 3408 maximum diversity and coding gain are illustrated by simulating an optimal interleaver Duration Tu 448 µs with convolutional coding, illustrated in Fig. 6c, which shows approximately 5 dB code Carrier spacing 1/ Tu 2232 Hz gain for the system with two transmit antennas. Spacing between carriers K min 7.61 MHz and Kmax CONCLUSIONS In this article the principles of delay diver- Allowed guard interval τ/ T 1/41/8 1/16 1/32 u sity, cyclic delay diversity, phase diversity, and maximum ratio combining have been Duration of symbol part Tu 4096 x T 448 µs discussed. The equivalence between cyclic delay diversity and phase diversity has been 1026 x T 512 x T 256 x T 128 x T identified. The application of CDD to a Duration of symbol interval τ DVB-H system has been simulated. CDD 112 µs 56 µs 28 µs 14 µs can potentially achieve spatial diversity and coding gain of at least 5 dB. CDD is an Symbol duration Ts = τ +Tu 560 µs 504µs 476 µs 462 µs elegant low-cost transmit diversity technique for coded OFDM that can provide I Table 1. OFDM parameters for the 4k mode. full spatial and coding diversity. CDD could potentially be accommodated by existing broadcasting systems without changing the SIMULATIONS standards or receivers, and the number of transmit antennas appears to be arbitrary. In this section we present simulation results for CDD presents a potential open diversity archi- DVB-H performance with antenna diversity in tecture for future broadband wireless broadcast typical urban (TU) and rural area (RA) using a networks. UHF (900 MHz) frequency channel. The simulations include Doppler effects and are according REFERENCES to the Monte Carlo method. The overall trans- [1] ETSI, “Digital Video Broadcasting (DVB); Framing Struc- mitted power is the same for all simulation runs, ture, Channel Coding and Modulation for Digital Ter- and the total transmit power from N antennas is restrial Television,” July 1999, EN 300 744 V1.2.1. equal to the transmit power with 1 antenna; the [2] S. B. Weinstein and P. M. Ebert, “Data Transmission by Frequency Division Multiplexing Using the Discrete power per transmit antenna decreases as the Fourier Transform,” IEEE Trans. Commun., vol. COM-19, number of antennas N increases. The antennas no. 15, Oct. 1971, pp. 628–34. are placed such that their channel transfer func- [3] R. van Nee et al., “New High-Rate Wireless LAN Stan- tions can be considered uncorrelated. A maxi- dards,” IEEE Commun. Mag., Dec. 1999, pp. 82–88. [4] J.-C. Guey et al., “Signal Designs for Transmitter Diversi- mum of two antennas were used at the ty Wireless Communication System over Rayleigh Fad- transmitter and receiver sides for these simula- ing Channels,” Proc. VTC ’96, pp. 136–40. tions. A cyclic delay of [5] V. Tarokh, N. Seshadri, and A. Calderbank, “Space-Time Codes for High Data Rate Wireless Communications: T 1 δµµ=1516⋅≈u . s ≥≈013. s Performance Criterion and Code Construction,” IEEE cy K B Trans. Info. Theory, vol. 44, Mar. 1998, pp. 744–65. [6] S. Alamouti, “A Simple Transmitter Diversity Scheme for was chosen for the BER vs. SNR simulations of Wireless Communications,” IEEE JSAC, vol. 16, Oct. the 2TX-antenna CDD systems, and the velocity 1998, pp. 1451–58. [7] A. Dammann and S. Kaiser, “Transmit/Receive Antenna of the mobile user is 10 m/s. Diversity with MRC Diversity Techniques for OFDM Systems,” Euro. Trans. is assumed at the receiver. Figure 6a shows the Telecommun., vol. 13, no. 5, Sept.–Oct. 2002, pp. 531–38. BER vs. SNR for a channel in a simulated TU [8] ETSI, “Digital Video Broadcasting (DVB); DVB-H Imple- scenario with CDD applied to the DVB-H sys- mentation Guidelines,” Feb 2005, TR 102 377 V1.1.1. [9] J. Heiskala and J. Terry, OFDM Wireless LANs: A Theo- tem, in 4k mode with 4-quadrature amplitude retical and Practical Guide, Sams, Dec. 2001. modulation (QAM) and code rate 1/2 in UHF. A single-antenna system with no spatial diversity BIOGRAPHIES is given as a reference. According to Fig. 6a, the system with receiver YUE ZHANG ([email protected]) studied telecommu- cation engineering at Beijing University of Posts and MRC outperforms a single-receive--antenna sys- Telecommunications, P.R. China, and received B.Eng. and tem by about 6 dB, helped by the fact that the M.Eng. degrees in 2001 and 2004, respectively. In 2004 he second receive antenna provides additional sig- was a Ph.D. student in the Department of Electronic and nal power. In the case of transmit diversity in a Computer Engineering, Brunel University, United Kingdom. He is currently a research assistant of the Networks and TU channel, there is about 4 dB gain in SNR at Multimedia Communications Centre at Brunel University. –4 a BER of 2 × 10 . The powerful channel codes His research interests are digital signal processing, space-

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0.1 0.1 CDD 2Tx/2Rx typical urban UHF CDD 1Tx/2Rx typical urban UHF CDD 2Tx/1Rx typical urban UHF CDD 1Tx/1Rx typical urban UHF 0.01 0.01

1E-3

1E-3 1E-4 Bit errror rate Bit errror rate

1E-5 CDD 2Tx/2Rx RA UHF CDD 2Tx/1Rx RA UHF 1E-4 CDD 1Tx/2Rx RA UHF CDD 1Tx/1Rx RA UHF 1E-6 4 6 8 10 12 14 2 4 6 8 10 12 14 16 18 SNR dB SNR dB A B

10-1 RX1/TX1 without interleaver RX1/TX2 without interleaver RX1/TX2 with interleaver

10-2 rate ror er

Bit 10-3

10-4 7 8 9 10 11 12 13 14 15 16 17 SNR dB C

I Figure 6. Simulation results.

time coding, MIMO, radio propagation models, multimedia ness providing GPS simulators to a world market before and wireless networks, and DVB-T/H. moving on to establish a new fixed wireless product line that deployed 1million lines around the world. He left to JOHN COSMAS [M’87] ([email protected]) join PipingHot Networks in 2000, a wireless startup that is obtained a B.Eng. honors degree in electronic engineering now established as an international provider of non-line-of- at Liverpool University in 1978 and a Ph.D. in image pro- sight radio links using similar principles to those proposed cessing and pattern recognition at Imperial College in here. More recently he has been working as an indepen- 1987. He is a professor of multimedia systems and dent consultant in the wireless, broadcast, and GPS indus- became Member of IEE in 1977. His research interests are tries. concerned with the design, delivery, and management of new fourth-generation TV and telecommunications ser- YONG-HUA SONG [SM] received his B.Eng., M.Sc., and Ph.D. vices and networks, multimedia content and databases, in 1984, 1987, and 1989, respectively. In 1991 he joined and video/image processing. He has contributed toward Bristol University, and then held various positions at Liver- eight EEC research projects, and has published over 80 pool John Moores University and Bath University before he papers in refereed conference proceedings and journals. joined Brunel University in 1997 as professor of network He leads the Networks and Multimedia Communications systems in the Department of Electronic and Computer Centre within the School of Engineering and Design at Engineering. Currently he is director of tje Brunel Advanced Brunel University. Institute of Network Systems and pro-vice-chancellor of the university. He has published four books and over 300 MAURICE BARD graduated from Imperial College in 1976 papers mainly in the areas of applications of intelligent with a B.Sc. (Hon) in materials science and worked initially and heuristic methods in engineering systems. He was on traveling wave tube design, electronics systems, and awarded the Higher Doctorate of Science in 2002 by software. He has succeeded in a number of engineering, Brunel University for his significant research contributions. sales and marketing roles during a 20-year career at Nortel He is a fellow of the IEE and the Royal Academy of Engi- Networks. While there he founded and managed a busi- neering.

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