Chadi Khirallah

Image-in-image hiding using complete complementary sequences

This paper addresses a data-hiding problem where a source image needs to be hidden into another host image. We consider both cases when the decoder has access to the host image (non-blind data-hiding), and when the decoder does not (blind data-hiding). Our proposed solution combines complete complementary (CC) spreading sequences and nested scalar quantization (NSQ). To enhance security, the source image is encrypted prior to embedding. Our simulation results, for both non-blind and blind data-hiding, with AWGN attacks show competitive results. Indeed, for blind data-hiding, our design outperforms the traditional NSQ system by 8 dB.

Multiterminal source coding for multiview images under wireless fading channels

This paper addresses the problem of wireless transmission of a captured scene from multiple cameras, which do not communicate among each other, to a joint decoder. Correlation among different camera views calls for distributed source coding for efficient multiview image compression. The fact that cameras are placed within a short range of each other results in a high level of interference, multipath fading, and noise effects during communications. We develop a novel two-camera system, that employs multiterminal source coding and complete complementary data spreading, so that while the former technique exploits the statistical correlation between camera views, and performs joint compression to reduce transmission rates, the spreading technique will protect transmitted data by mitigating the effects of wireless fading channels. Our results indicate that the proposed system is competitive when compared to two independently JPEG encoded streams at low to medium transmission rates.

Network Spread Coding

Data streaming over wireless ad hoc and peer-to- peer networks faces the problem of high level of inference, fading, and noise, which limits the feasibility of attractive realtime multimedia applications. One classical solution to reduce those effects is to employ the spread spectrum technique, which usually leads to unacceptable increase in the required bandwidth. On the other hand, network coding has recently been proposed as an efficient method for bandwidth reduction. In this paper, we describe a complete complementary coding based scheme, termed network spread coding (NSC) that brings together spread spectrum and network coding. NSC offers robustness to inference and noise, together with reduction in the required bandwidth. We develop two practical NSC designs that show competitive or better performance with respect to traditional spread spectrum schemes at lower complexity while achieving huge bandwidth savings both in AWGN and fading channels.

Compress-spread-forward with multiterminal source coding and complete complementary sequences

We propose a new technique, compress-spread forward (CSF), for high-performance wireless streaming from two base stations in parallel. CSF uses multiterminal source coding for efficient source compression and complete complementary sequences for error-free multiple access and synchronization. Our practical design shows significant performance gains due to spatial diversity and distributed source coding.

Bandwidth efficient multi-station wireless streaming based on complete complementary sequences

Data streaming from multiple base stations to a client is recognized as a robust technique for multimedia streaming. However the resulting transmission in parallel over wireless channels poses serious challenges, especially multiple access interference, multipath fading, noise effects and synchronization. Spread spectrum techniques seem the obvious choice to mitigate these effects, but at the cost of increased bandwidth requirements. This paper proposes a solution that exploits complete complementary spectrum spreading and data compression techniques jointly to resolve the communication challenges whilst ensuring efficient use of spectrum and acceptable bit error rate. Our proposed spreading scheme reduces the required transmission bandwidth by exploiting correlation among information present at multiple base stations. Results obtained show 1.75 Mchip/sec (or 25%) reduction in transmission rate, with only up to 6 dB loss in frequency-selective channel compared to a straightforward solution based solely on complete complementary spectrum spreading.

Low complexity multi-view video streaming over multipath fading channels

This paper addresses the problem of wireless delivery of a captured scene from multiple cameras, which do not communicate among one other, to a joint decoder. Correlation among different camera views calls for distributed source coding for efficient compression. The fact that the cameras may be placed within a short communication range of each other results in a high level of interference, multipath fading, and noise effects, during transmission. We develop a new two-camera system, where one camera employs H.264 SVC, whereas the other, low-complexity camera codec exploits statistical dependencies between closely-located cameras views to jointly perform compression and spreading using Complete Complementary (CC) sequences for protection against interference. This paper proposes a very low complexity scalable coding scheme using fixed integer Discrete Cosine Transform (DCT) and fixed quantizer matrices instead of the 2D DCT. The proposed system is targeted at wireless multi-view video streaming applications, in which the data acquired form different viewing cameras are highly correlated spatially and temporally. Our results indicate that our proposed system is competitive with H264 SVC coded streams.

Stereo Image Transmission over Fading Channels with Multiterminal Source Coding

This paper addresses the problem of wireless delivery of a captured scene from two cameras, which do not communicate with each other, to a central point for joint decoding. We exploit correlation among two camera views using distributed source coding and use complete complementary (CC) data spreading to combat multiple access interference and noise even when the transmitters are de-synchronized. Our distributed source coding scheme is based on uniform scalar quantization in the DCT domain and non-asymmetric Slepian-Wolf coding via turbo codes. The non-asymmetric Slepian-Wolf scheme enables efficient trade-off between the transmission rates of the two cameras. Simulation results indicate that the proposed system outperforms significantly two independently JPEG-encoded streams at low transmission rates.

A fixed point DSP implementation of a novel MIMO P2P radio link

In this paper we present the performance of DSP implementation for VBLAST receiver design used in our previously proposed enhancement of a P2P radio system. The system proposed uses a cochannel dual spatial dual polarisation mode allowing the transmission of 622 Mbps STM4 signals on four subchannels. Previously we have presented results using a LMS interference canceller at the receiver which, although it successfully cancelled the major interference effects, it did not fully utilise the possible diversity gains offered by this novel system configuration, or included the effects of fading in the channel. In this paper we present results from DSP implementations of both the existing system and a new receiver structure which employs both a MRC and ZF-VBLAST. The results show that a fixed point arithmetic implementation of the ZF-VBLAST receiver is able to give a 10 dB improvement in system performance for an increase in complexity of 1.2 times that of the floating point arithmetic LMS receiver.