Peter Cherriman

Interactive cellular and cordless video telephony: State-of-the-art system design principles and expected performance

Second-generation (2G) mobile radio standards have not been designed with video communications in mind, although the employment of error-resilient, constant-bit-rate proprietary video codecs over these systems is realistic. The third-generation (3G) systems are capable of providing higher rates and better communications integrity in support of video applications. This paper advocates the employment of burst-by-burst adaptive transceivers, which are capable of accommodating the time-variant channel quality fluctuation of wireless channels. This paper is concluded with a range of performance figures and system design guidelines for wireless systems.

Orthogonal frequency-division multiplex transmission of H.263 encoded video over highly frequency-selective wireless networks

The video performance of a 155-Mbps wireless asynchronous transfer mode (WATM) proposal and that of a 2-Mbps Universal Mobile Telecommunications System (UMTS) concept is evaluated for a range of low- to high-quality video application scenarios, various propagation conditions, and video bit rates using the H.263 video codec, assisted by a novel packetization and packet acknowledgment scheme. Orthogonal frequency-division multiplexing is invoked over the highly dispersive channels for conveying high-rate video signals. Various binary Bose-Chaudhuri-Hochquenghem and turbo codes are investigated comparatively, with the conclusion that due to the high error resilience of the video packetization and acknowledgment scheme, the increased power of the higher complexity turbo codec does not translate to substantially improved overall system robustness, although the bit error rate and acknowledgment flag error rate are significantly reduced. The whole range of video resolutions and system parameters is summarized in a number of tables. The required channel signal-to-noise ratio for near-unimpaired video quality is about 16 dB for the inherently lower quality, lower resolution video frame formats, but slightly higher, about 18 dB, for the high-definition formats, where the error-induced subjective video degradations become more objectional over the highly dispersive worst case channels used.

Turbo- and BCH-coded wide-band burst-by-burst adaptive H.263-assisted wireless video telephony

The video performance benefits of burst-by-burst adaptive modulation are studied, employing a higher-order modulation scheme when the channel is favorable, in order to increase the systems bits per symbol capacity and conversely, invoking a more robust lower order modulation scheme when the channel exhibits inferior channel quality. It is shown that due to the proposed adaptive modem mode switching regime, a seamless video quality versus channel quality relationship can be established, resulting in error-free video quality right actress the operating channel signal-to-noise ratio (SNR) range. The main advantage of the proposed burst-by-burst adaptive transceiver technique is that irrespective of the prevailing channel conditions, the transceiver achieves always the best possible source-signal representation quality-such as video, speech, or audio quality-by automatically adjusting the achievable bit rate and the associated multimedia source-signal representation quality in order to match the channel quality experienced. This is achieved on a near-instantaneous basis under given propagation conditions in order to cater for the effects of path loss, fast-fading, slow-fading, dispersion, co-channel interference, etc. Furthermore, when the mobile is roaming in a hostile out-doors-or even hilly terrain-propagation environment, typically low-order low-rate modem modes are invoked, while in benign indoor environments, predominantly the high-rate high source-signal representation quality modes are employed.

Subband-adaptive turbo-coded OFDM-based interactive video telephony

A range of adaptive orthogonal frequency division multiplex (AOFDM) video systems are proposed for interactive communications over wireless channels. The proposed constant target bit-rate subband-adaptive OFDM modems can provide a lower bit error rate than a corresponding conventional OFDM modem. The slightly more complex switched or time-variant target bit rate AOFDM modems can provide a balanced video quality performance, across a wider range of channel signal-to-noise ratios, maintaining the best video performance. Upon invoking the technique advocated, irrespective of the channel conditions experienced, the transceiver achieves always the best possible video quality by automatically adjusting the achievable bit rate and the associated video quality in order to match the channel quality experienced. This is achieved on a near-instantaneous basis under given propagation conditions in order to cater for the effects of path-loss, fast-fading, slow-fading, dispersion, etc. Furthermore, when the mobile is roaming in a hostile outdoor propagation environment, typically low-order, low-rate modem modes are invoked, while in benign indoor environments predominantly the high-rate, high source-signal representation quality modes are employed.

Burst-by-burst adaptive decision feedback equalized TCM, TTCM, and BICM for H.263-assisted wireless video telephony

Decision feedback equalizer-aided wide-band burst-by-burst adaptive trellis-coded modulation, turbo trellis-coded modulation (TTCM), and bit-interleaved-coded modulation-assisted H.263-based video transceivers are proposed and characterized in performance terms when communicating over the COST 207 typical urban wide-band fading channel. Specifically, four different modulation modes, namely 4QAM, 8PSK, 16QAM, and 64QAM are invoked and protected by the above-mentioned coded modulation schemes. The TTCM assisted scheme was found to provide the best video performance, although at the cost of the highest complexity. A range of lower-complexity arrangements will also be characterized. Finally, in order to confirm these findings in an important practical environment, we have also investigated the adaptive TTCM scheme in the CDMA-based universal mobile telecommunications systems terrestrial radio access (UTRA) scenario and the good performance of adaptive TTCM scheme recorded when communicating over the COST 207 channels was retained in the UTRA environment.

Error-rate-based power-controlled multimode H.263-assisted video telephony

The performance of a power-control algorithm suitable for multimode transceivers is investigated using 1, 2, and 4 bit/symbol modems. It is shown that the algorithm is suitable for maintaining a target frame error-rate (FER), irrespective of the modulation mode employed. The transceiver parameters are summarized in Table I, while the minimum and maximum required average transmitted powers in the cell for the different modes are given in Table V. Given the video bit rates of 4.25-16.9 kbps in the various modem modes, the corresponding average video peak signal-to-noise ratio (PSNR) improvement of approximately 6 dB can be inferred from the figure included, where the corresponding PSNR values are approximately 32.5, 35, and 38.5 dB, respectively. This PSNR improvement is achievable in cell areas, where the average transmitted power levels of Table V can be maintained, supporting one of the above legitimate modes of operation of the multimode transceiver.

Burst-by-burst adaptive wideband wireless video telephony

The design trade-offs of interactive wireless video systems are discussed and performance comparisons are provided both in the context of second- and third-generation wireless videophone systems. We commence our discussions by a comparative study of arbitrarily programmable, but fixed-rate, videophone codecs using quarter common intermediate format (QCIF) video sequences scanned at 10 frames/s. These proprietary codecs were designed to allow direct replacement of mobile radio voice codecs in second generation wireless systems, such as the Pan-European GSM, the American IS-54 and IS-95 as well as the Japanese systems, operating at 13, 8, 9.6 and 6.7 kbps, respectively, although better video quality is maintained over higher-rate, 32 kbps cordless systems, such as the Japanese PHS and the European DECT and CT2 systems. From the range of codecs investigated, best overall performance was achieved by our vector-quantised codecs, followed by the discrete cosine transformed and the quadtree-based schemes. The associated video peak signal-to-noise ratio (PSNR) was around 30 dB, while the subjective video quality can be assessed under http://www-mobile.ecs.soton.ac.uk. A range of multimode wireless transceivers is also proposed. The second part of the paper is dedicated to burst-by-burst (BbB) adaptive wireless video transceivers employing the standard H.263 codec. It is demonstrated that the proposed BbB adaptive transceivers provide an improved video performance in comparison to their statically reconfigured counterparts in the context of both wideband BbB adaptive quadrature amplitude modulation (AQAM) transceivers and the joint-detection based code division multiple access (CDMA) transceivers of the third generation systems.

Channel-adaptive wideband wireless video telephony

The fundamental advantage of burst-by-burst (BbB) adaptive intelligent multimode multimedia transceivers (IMMTs) is that-irrespective of the propagation environment encountered-when the mobile roams across different environments subject to path loss; shadow- and fast-fading; co-channel-, intersymbol-, and multiuser interference, while experiencing power control errors, the system will always be able to configure itself in the highest possible throughput mode, while maintaining the required transmission integrity. Finding a specific solution to a distributive or interactive video communications problem has to be based on a compromise in terms of the inherently contradictory constraints of video quality, bit rate, delay, robustness against channel errors, and the associated implementational complexity. Considering some of these tradeoffs and proposing a range of attractive solutions to various video communications problems is the basic aim of this overview. The article portrays a range of proprietary video codecs and compares them to some of the existing standard video codecs. A number of multimode video transceivers are also characterized. Systems employing the standard H.263 video codec in the context of wideband BbB adaptive video transceivers are examined, and the concept of BbB-adaptive video transceivers is then extended to CDMA-based systems.

Robust H.263 video transmission over mobile channels in interference limited environments

The cellular channel capacity of conventional cells is shown to vary dramatically as a function of the distance from the base station. An intelligent 7.3 kBaud adaptive videophone transceiver is contrived, in order to exploit the higher channel capacity of uninterfered cell areas and to satisfy the prevalent system optimisation criteria. The system employed an enhanced H.263-compatible video codec and it was capable of operating over a wide range of operating conditions. The proposed technique has the potential to support videotelephony over existing and future wireless systems using the H.263 video codec.

Dynamic channel allocation techniques using adaptive modulation and adaptive antennas

This contribution studies the impact of adaptive modulation (AQAM) on network performance, when applied to a cellular network using adaptive antennas with fixed channel allocation (FCA) and locally distributed dynamic channel allocation (DCA) schemes. The performance advantages of using adaptive modulation are quantified in terms of overall network performance, mean transmitted power and the average network throughput. With the advent of AQAM 33% and 87% increases in the number of users can be supported by FCA and DCA, respectively.