Wireless Broadband Multimedia Communications

Dubrovnik, September 22, 1997

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Wireless Broadband Multimedia Communication Branka Zovko-Cihlar, Sonja Grgic, Mislav Grgic Department of Radiocommunications and Microwave Engineering, Faculty of Electrical Engineering and Computing, Unska 3, 10000 Zagreb, Croatia [email protected] Abstract. The paper presents an analysis of wireless broadband multimedia communications as a wordwide interesting technology solution in modern communication applications. From several starting points indicates solutions towards the target UMTS, and investigates cooperation between existing systems as IN, GSM, Satellite systems and ATM. The field of broadband access systems services and network for wireless communication is still under development and researches, and we can expect improvement in the field of multimedia wireless communications. I.

Introduction

Developments in modern communication are proceeding the ongoing evolution of the worldwide wireline infrastructure toward increasing support for broadband multimedia services. Some basic aspects which distinguish wireline from wireless communications are: • the radio spectrum and capacity available for wireless access service is generally limited by ragulation, • wireline communications can easily be extended by developing additional wire or fiber facilities. Wireless Broadband Communication System (WBCS) provide its users a means of radio access to broadband services on customer premises networks or offered directly by public fixed networks. WBCS will provide a mobile nonwired extension to wired networks for information rates exceeding 2 Mb/s. WBCS will be wireless extension to the B-ISDN, achived with the transmission of ATM cells. The research in the field of WBCS has drawn a lot of attention because of the increasing role of multimedia and computer applications in communications. To implement WBCS it must be considered the frequency allocation and selection, channel characterization, application and environment recognation, air interface multiple access techniques, protocols and networks, systems development with efficient modulation, coding and antena techniques. Modular and layered concepts based on standardized network and service bilding blocks will provide the universal and economic solutions. These concepts will be supported by flexibl and bitrate-independent ATM network. ATM networks are being introduced internationally in the private and public areas, to support fixed and mobile, narrowband and broadband communications in several steps. The specific areas which have been studied, is Universal Mobile Telecommunications Systems (UMTS) bodies are services, charging and accounting, switching and signaling and network operations and management.


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In multimedia communications image data compression is very important issue, especially in transmission and storage of image data. Its aim is to minimize the bandwidth for transmission and the memory for storage. The MPEG standards for video coding adresses the combining of more elementary streams of video, audio, text, still pictures, graphics and other data into a single or multiple streams which are suitable for transmission, storage and users interaction. Using these possibilities, the basic audio-visual contents can be rearranged with very powerful multimedia additions in a variety of environments.

II.

Video Compression Standards

Image data compression is very significant problem in communications, multimedia and broadcasting. Modern data compression techniques offer the possibility to store or transmit great amount of data necessary to represent digital images and video in an efficient way. The importance of these techniques arise in the world, where productivity gains through communications depend on the mobility, flexibility and interoperability of communication equipment - where everybody will be able to communicate with anybody at any place and at any hour. Video coding is one of the key technologies in this multimedia era and its standardisation is essential for efficient interchange of audio-visual information. Several standards bodies have been working on algorithms to compress video. There are now four worldwide unique video standards which are widely supported: ISO/IEC 10198 (so called JPEG), ITU-T Rec. H.261, ISO/IEC 11172 (MPEG-1), and ITU-T Rec. H.262\ISO/IEC 13818 (MPEG-2) for different bit rates and applications, Tab. I. Tab. I. Video Coding Standards Name

Typical Image Format

Video Source Rate Coded Bit Rate

JPEG H.261 MPEG-1 MPEG-2 MPEG-4

still picture (max.size 4096x4096 pels) CIF | QCIF SIF CCIR 601 QCIF

8 b/pel 36 Mb/s | 9 Mb/s 30 Mb/s 166 Mb/s 166 Mb/s

0.25...2.25 b/pel px64 kb/s, 1≤p≤30 1.2 Mb/s 4...9 Mb/s 5…64 kb/s

Image compression and video-coding algorithms can be generally divided into two broad categories: intraframe and interframe coding. Intraframe coding is used to remove spatial redundancy between the picture elements (pels) in single frame. Interframe coding takes advantage of the strong correlation among video frames to reduce the temporal redundancy. In H.261, MPEG-1 and MPEG-2 standards, both spatial and temporal redundancy reduction are used together in order to achieve the highest possible compression ratio between the video source rate and the coded bit rate. The Joint Photographic Experts Group (JPEG) of the ISO specified coding scheme for still picture coding. The basic scheme is adaptive Discrete Cosine Transform (DCT) coding. A specified average transmission rate can be adjusted by quantizer characteristic but this also affects the picture quality.


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The International Telecommunication Union (ITU, formerly CCITT) specified the H.261 standard entitled ”Video codec for audio-visual services at px64 kbit/s” as a video coding standard for videoconferencing and videophone. The format for input picture is based on the common intermediate format (CIF). The ISO/IEC activity of the MPEG was started in 1988 for CD-ROM applications at a bit-rate below 1.5 Mb/s. CD-ROMs are considered as a promising storage medium for multimedia video applications. The MPEG-1 coding scheme is very similar to that of ITU-T H.261. The major difference between the two is that MPEG-1 allows bi-directional motioncompensation The recommended input picture format is Source Input Format (SIF). The MPEG SIF is compatible to CCIR Rec.601 (now ITU-R Rec.601) picture format, see Tab. 2. CCIR Rec. 601 is universal adopted standard which defines an extensible family of the coding parameters for NTSC/PAL television signal. Tab. II. Conversion of Image Formats Picture Rate [Hz] Luminance CCIR Sample Resolution SIF Sample Resolution Colour difference (CB, CR ) CCIR Sample Resolution SIF Sample Resolution

30

25

720 x 480 360 x 240

720 x 576 360 x 288

360 x 480 180 x 120

360 x 576 180 x 144

MPEG-1 standard was originally developed for storage of full-motion video, but this standard can provide a broader range of applications due to its parameterisation approach. MPEG-1 standard can be used for interactive video and provides a picture quality comparable to VCR (Video Cassette Recorder) picture quality. However, its quality and flexibility are considered not ideal enough for the higher quality and higher bit-rates applications such as broadcast TV and High Definition Television (HDTV). To meet these requirements, the MPEG-2 project was started. The ongoing effort of MPEG is the ISO/IEC working group JTC1/SC29/WG11, but MPEG-2 has been working jointly with the ITU-T Study Group 15 "Experts group for ATM Video Coding”. Because of the wide range of applications, MPEG-2 is a family of standards with different profiles and levels. This approach decorrelates the coding algorithm from the application dependent parameters and becomes important platforms for the further development of the multimedia interactive communication. Roughly speaking, coding algorithms conforming to the MPEG-1 and MPEG-2 standards are similar, i.e., motion-compensated interframe coding schemes using DCT and both forward and backward predictions. The main difference between MPEG-1 and MPEG-2 is that MPEG-1 has been optimised for noninterlaced (progressive) format while MPEG-2 is a generic standard (application independent) for both interlaced and progressive formats with more sophisticated prediction schemes considering field based modes. The MPEG-2 is optimised for CCIR 601 interlaced image sources with minimal loss of efficiency for other formats


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A. MPEG-2 Systems Solutions The principle features of the MPEG-2 standard is the capability to support different applications and picture parameters all under umbrella of the same MPEG-2 Video Syntax by means of profiles and levels. The profile can be seen as a subset of the entire bitstream syntax and the level as a set of constraints imposed on parameters in the bitstream. The full video syntax can be divided into two major categories: the non-scalable and scalable syntax. The non-scalable syntax gives the extra compression tools for interlaced video signals. Each frame of interlaced video consists of two fields which are separated by one field period. The specification allows either the frame to be encoded as picture or the two fields to be encoded as two pictures. Frame encoding or field encoding can be adaptive selected on a frame-byframe basis. Frame encoding is typically preferred when the video scene contains significant detail with limited motion. Field encoding, in which the second field can be predicted from the first, works better when there is fast movement. The MPEG-2 includes the possibility to insert in its bit-streams multimedia and hypermedia information objects which are defined by Multimedia and Hypermedia Experts Group (MHEG) of ISO/IEC SC29. This group produces standard ”Information Technology Coded Representation of Multimedia and Hypermedia Information Objects” which specifies the representation and encoding of multimedia objects, i.e. the aggregation of monomedia data such as text, still pictures, graphics, audio and video sequences, the control of their presentation, synchronisation and user interaction. An MHEG objects can be interchanged as a whole across different applications/services. B. Coding Algorithm The main processing step for MPEG coding is macroblock-based motion compensation in the interframe coding and block-based DCT in intraframe coding. In the intraframe-coding mode, the frame is processed block by block. The source image is divided into 8x8 pixel blocks and every block is transformed to a 64 point discrete signal which is function of two spatial dimensions. A two-dimensional DCT is applied to all luminance and chrominance blocks in frame. The aim of the transform is to take advantage of the correlation between samples within the block. The 8x8 size is presently widely considered to be the most convenient compromise between efficiency and implementation complexity. Mathematical expression of the forward DCT and inverse transform is expressed by the following equation, where z(i,j) are samples in the image domain, and Z(k,l) are coefficients of the transform block:

(

Z k, l

( )

z i, j

C k ,l

)

1

= =

4 1 4

⋅

7

⋅Ck ⋅Cl ⋅∑ i

7

7

∑ ∑ Ck

k

=0

l

=0

=0

7

∑ z(i, j)

⋅ cos

j=0

⋅ C l ⋅ Z (k, l) ⋅ cos

π⋅(2⋅i +1)⋅k 16

π⋅(2⋅i +1)⋅k 16

⋅ cos ⋅ cos

π⋅(2⋅j +1)⋅l 16

π⋅(2⋅j +1)⋅l

(1)

16

 1 , for k,l= 0  =  2   1 , else

The result is 8x8 block of DCT coefficients. Each coefficient represents the amplitude of the specific pattern within the block, and applying the transform, the original picture block is expressed as a two-dimensional series in terms of this set of orthogonal patterns. The first


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coefficient is DC coefficient and it is proportional to the average value of the of the pel values in the block. Therefore, the DC coefficient is more visually significant then the other coefficients The remained 63 coefficients are called AC coefficients and they represent horizontal frequency components, vertical frequency components or both horizontal and vertical frequency components. The DCT coefficients are fed into a quantizer .The step size for the quantization of each DCT coefficients is obtained from an 8x8 quantizer matrix which ensures that the low frequency DCT coefficients are quantized more accurately (with small step size) while the high frequency coefficients are quantized more coarsely. C. MPEG-4 Systems Solutions Current MPEG standardization project is MPEG-4. ISO MPEG-4 started its standardization activities in July 1993 and MPEG-4 will became International Standard in November 1998. It can be expected that MPEG-4 will became the enabling technology for multimedia communications as much as MPEG-2 has become the enabling technology for digital television. MPEG-4 will be a genreic video coding algorithm mainly targeted for a wide range of low bit rate multimedia applications. It is generally expected that the delivery of video information over existing and future low-bandwidth communication network such as mobile radio networks or telephone networks will become very important. The success of audiovisual services operating over mobile or telephone networks (in the market place) will depend on the ability to encode video at very low bit rates with sufficient image quality. Existing video coding standards (e.g. H.261 and MPEG-1) have been optimized to achieve good video quality at bit rates higher than 64 kb/s. Accordingly the video quality provided by these algorithms is not sufficient for application realised at very low bit rates. MPEG-4 will standardize algorithms for audiovisual coding in multimedia applications allowing for interactivity high compression and universal accessibility of audio and video content. Bit rates targeted for the video standard are between 5÷64 kb/s for mobile applications and up to 2 Mb/s for TV-film applications. With the respect to existing standard seven new video functionalities have been defined, Tab. III. Tab. III. MPEG-4 functionalities Content based interactivity • content based manipulation and bit stream editing • hybrid natural and synthetic data coding • improved temporal random access

Compression • improved coding efficiency • coding of multiple concurent data streams

Universal access • robustness in error-prone environments • content-based scalability


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In MPEG-1 and MPEG-2 standards the video information is assumed to be rectangular of fixed size. In MPEG-4 the concept of video object (VO), video object layer (VOL) and video object plane (VOP) have been introduced. VO and VOP correspond to entities in the bit stream that a user can access and manipulate (VOP can have arbitrary shape!). Together with VOP composition information is sent to indicate where and when each VOP is to be displayed. At the decoder side the user may be allowed to change the composition of the scene by interacting on the composition information. The shape, motion and texture information of the VOP's are coded and transmited using the same algorithm which is similar to the successful MPEG-1/2 or H.261 algorithms. It is based on block-based hibrid DPCM/transform coding technique. MPEG-4 standard will support multimedia communications allowing interactivity, high compression and universal access. III.

Wireless Network and Service Evolution

The extension of mobile systems to broader bandwidths and richer variety of services have been explored in activities around the world and is described with the Fig. 1. First generation Mobile telephone Service: carphone Analog cellular technology Macrocellular systems

Second generation Digital voice + messaging/data services Fixed wireless loop

Third generation Fourth generation Integrated high-quality audio and data; TelePresencing

Past Digital cellular technology + IN emergence Microcellular and picocellular; capacity, quality; LANs Enhanced cordless technology

Now

Narrowband and broadband multimedia services + IN integration

Broader bandwidth Efficient radio transmission; LAN/WAN; information compression

Education, training, and dynamic information access

Wireless-wireline and broadband transparency

Higher frequency spectrum utilization: LAN/WAN

Knoledge-based network operations

IN + network management integration

Unified service network

Year 2000

Year 2010

Fig. 1. Generations of wireless communications


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On the Fig. 1. is shown relations and differences of concepts being rooted in data communications and telecommunications, with special attention to the future role of ISO/OSI reference model. The wireless access technology will introduce evolution and maintain high quality of service that the communications and television industries already provided. The broadcast television has provided broadband access to the televised broadcast media with terrestrial radio transmission or via satellite system. Other form is Wireless Local Area Network (WLAN), completely digital. It is most efficient at connecting portable computing and data entry systems to a LAN. WLANs can be categorized as providing low-mobility, high speed, data communications within a confined region (campus or large building). Some of WLANs in bilding has very limited distance. Advance in technology solution is that the televised media has been driven into cable distribution systems, allowing a larger number of entertaiment channels. On this way is eliminated large external antenas in urban areas. This systems promise interactive two-way connectivity for data and Internet services. Tab. IV. Broadband services Broadband digital service Broadcast video Bradcast TV Enhanced pay per view Interactive video Video on demand Interactive TV Interactive games Information retrieval services Internet access (www, FTP, Telnet) voice broadcast Symmetric data Desktop multimedia Work-at-home Video conferencing Video telephony Fax Small business/home Internet home page Internet information server

Downlink bandwidth

Uplink bandwidth

1.5 to 6 Mb/s per channel

None or POTS (telephony)

64 kb/s to 6 Mb/s

9.6 to 64 kb/s

14.4 kb/s to over 10 Mb/s

14.4 kb/s to 128 kb/s

9.6 kb/s to 2 Mb/s

9.6 kb/s to 2 Mb/s

9.6 to 384 kb/s

64 kb/s to 1.5 Mb/s

Wireless LAN of few megabits per second will develop to ten and hunderts of megabits per second and TCP/IP protocol. This systems will occupy radio spectrum at microwave and milimeter wave frequencies. From Tab. IV. it is evident that the broadband services to be carried of some of these networks may each have their own traffic characteristics. Wireless multimedia will be driven mainly by Intranet and Internet access. The main success of a wireless networking is to provide connectivity rapidly with minimal infrastructure. The Tab. V. provides a comparison of the spectrum allocations, data rates and a range for indoor and outdoor wireless access systems.


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Tab. V. Comparation for indoor and outdoor wireless access systems

IV.

Parameter

Indoor

Outdoor fixed

Outdoor mobile

Spectrum

Licensed and unlicensed bands

Licensed bands

Licensed bands

RF and infrared

RF

RF

Date rate per user

5 to 150 MHz bandwidth 1 to 2 b/s/Hz

5 MHz to > 1GHz total bandwidth 0.5 to 2 b/s/Hz

5 to 30 MHz total bandwidth 0.1 to 0.25 b/s/Hz

Number of users per cell Cell range

1 to > 100 Mb/s Tens 60 m

64 kb/s to 2 Mb/s Hunderts 2 km

10 to 144 kb/s Tens 30 km

High-speed WLANs

WLANs are providing low-mobility high-speed data communications within confined region. Coverage is limited to within a room or to several rooms in a building what means that success has been limited. An IEEE standards committee 802.11, has been attempting to put some order into this process. The radio frequency range of such WLANs are 18-20 GHz, 2.4 GHz and 900 MHz. WLANs networking architecture is designed to deliver Virtual LANs with switching technology and distributed routing integrated into existing network infrastructure. This is centralised policy-based management to simplify the administration and control of network. WLAN development are primariliy directed towards using wireless components as LAN interfaces to wired backbones in dificult office environments. V.

Universal Mobile Telecommunications System (UMTS)

The European Telecommunications Standards Institute (ETSI) is looking for the definition on UMTS and parallel standardization activities are undertaken within ITU for the Future Public Land Mobile Telecommunication System (FPLMTS). The UMTS standardization begone at 1994 in ETSI’s Special Mobile Group 5 (SMG5). It is planed that the fix network supports both terminal mobility and personal mobility. Special technology fields are envolved in this standard such as UMTS framework services, radio interface, network platform, management and satellite systems. The detailed specificsation is expected at the end of 1998. This system will provide a wide range of services to mobile and stacionary users. UMTS will integrate services and networks and also requires a common users interface. UMTS envisage radio services providing up to 144 kb/s with extension to 20 Mb/s for various multimedia services. Service quality should at least be comparable to current fixed network services. The main parts of UMTS are: • the UMTS core network – switching, • the UMTS control network, • the UMTS radio access system.


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A. GSM Systems GSM networks represent an important basis for an evolution toward UMTS since the networks provide universal connectivity to UMTS. GSM based evolution scenario describes how the target UMTS can be achieved starting from the perspective of GSM operator. Development will go into parallel direction. One conserns the evolution of the radio access from GSM access via multimode GSM/DECT (DECT 1800 cellular networks in Europe and Australia) access toward UMTS access. The mobility management of GSM is used for this perposes. The other conserns the evolution of service control from GSM-based solutions towards Inteligent Network (IN) solution. IN functions and protocols will be used for the provision of both mobility management and supplementary IN services. B. Satellite System Evolution The important component of UMTS is the satellite communication which provide a specific radio access system for global coverage. The satellite system could act as an auxiliary to the terrestrial system. Mobile satellite has to satisfy GSM requirements and provides integration into GSM. There are important problems in reusing the mobility management procedures of GSM in the satellite system. Further, UMTS fuctionalities shall be introduced by eding new fuctional blocks, but some modifications of GSM functional blocks shall be performed. IN capabilities into satellite access network could be applied. C. Wireless ATM ATM technology is expected to become dominat networking technology for public and LANs infrastructure netowrks. Spectrum of wireless LANs has been allocated for high performance LAN at 5 GHz with connectivity of 20 to 25 Mb/s. It was moved to 40 and 60 GHz with 100 Mb/s and is still in current research. This high frequency offer large amount of spectrum and radio links required directional antenna. For this reason it is more convenient to use 900 MHz, 2.4 GHz and 5 GHz band, to have broader applicability. Wireless ATM with a wireless access system meets the needs for end-to-end networking infrastructure. A Wireless access point connects the set of wireless nodes on a single port of ATM switch. The system consists of wireless access points distributed in the building must be coverd, and a wired ATM network for connectivity to the wireless access point. That means for example one group of users share floor in a building. Local computing system is set of servers wired together via Fiber Distributed Data Interface (FDDI) and an ATM user premises switch. All users have notebook computers, most of them have voice capabilites and 20% have video capability. We can assume that six of users are involve in a voice plus data conection and 1 from 20 is involved in video connection. Wireless range of 20 m for wireless LAN with capacity of 10 to 25 Mb/s per access point area would be sufficient (6 Mb/s for data, 640 kb/s per voice, 6 Mb/s per video = 12.6 Mb/s).


VI.

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Conclusion

Wireless broadband multimedia communication will have an significant influence on the evolution of existing fixed and mobile comunication systems, particulary IN, B-ISDN, GSM, UMTS and ATM architecture. This will enable to send the voice, data and video within the very near future in both the private and public sectors with good quality. It is shown integratin and evolution of existing fixed and mobile communication system infrastructure towards UMTS in Europe. References [1]

Wallace G.K., “The JPEG still picture compression standard”, Comm.ACM, Vol.34, No.4, pp.31-44, Apr.1991 [2] ITU-T Recommendation H.261, “Video codec for audio-visual services at px64 kbit/s”, Dec.1990, Mar.1993 (revised) [3] ISO/IEC IS 11172-2, “Information Technology-Coding of Moving Picture and Associated Audio for Digital Storage Media at up to about 1.5 Mbit/s: Video”, Aug.1993 [4] ISO/IEC DIS 13818-2, “Information Technology-Generic Coding of Moving Pictures and Associated Audio Information: Video”, Draft, Mar.1994 [5] CCIR Recommendation 601, ”Encoding parameters of digital television for studios”, Recommendations and reports of the CCIR, XVII Plenary Assembly, Düsseldorf, 1990, Volume XI - Part 1 Broadcasting services [6] Garrett M.W., “A Service Architecture for ATM: From Applications to Scheduling”, IEEE Network, Vol.10, No.3, pp.6-14, May/June 1996 [7] Schwartz M., “Network Management and Control Issues in Multimedia Wireless Networks”, IEEE Personal Communications, Vol.2, No.3, pp.8-16, Jun.1995 [8] Magedanz T., “Integration and Evolution of Existing Mobile Telecommunications Systems toward UMTS”, IEEE Communications Magazine, Vol.34, No.9, pp.90-96, Sep.1996 [9] Zovko-Cihlar B., Bauer S., “Video Compression Standards and Multimedia Applications”, TD COST 242, Bratislava, Sep.1995 [10] Honcharenko W., Kruys J.P., Lee D.Y., Shah N.J., “Broadband Wireless Access”, IEEE Communications Magazine, Vol.35, No.1, pp.20-26, Jan.1997 [11] Acampora A., “Wireless ATM: A Perspective on Issues and Prospects”, IEEE Personal Communication, Vol.3, Nno.4, pp.8-17, Aug.1996 [12] Zovko-Cihlar B., Bauer S., Modric D., “Predictive and Transform Coding in Multimedia”, TD COST 242, Lousanne, Jan.1996