International telecommunication union

3.2 Performance improvement

RTL (register transfer level) simulation of triple DES processing shows the six times speed up when the R unit was used compared with when the R unit was not used.

With the method discussed above, custom instructions are defined to perform processing that would require a combination of large number of instructions if R-unit were not used. This means that the number of instructions required is reduced and, as a consequence, that the amount of instruction code becomes smaller. In case of triple DES processing, the program code size becomes less than one half when the R unit was used compared with when the R unit was not used.

4 Application to digital baseband processing

For instance, in Bluetooth baseband processing, error correction is based on a bit repetition of code rate of 1/3 or a shortened Hamming code (15,10) of code rate of 2/3. The first method is simply to transmit the same bit three times in succession. If the permutator in R-unit is used, send data would be created efficiently. A speed increase by 20 to 30 times will be expected when compared with the case where the R-unit is not used. The second method can be made faster about four times if LFSR (linear feedback shift register) processing can be performed. A speed increase by about three times will also be possible for CRC processing, scrambling, and other processing.

It can be said that this reconfigurable processor is also applicable to 3G or systems beyond IMT 2000, because those systems require many bit level data processing.

5 Conclusion

6 References

[2] H. Okano, et al, “An 8-Way VLIW Embedded Multimedia Processor Built in 7-Layer Metal 0.11um CMOS Technology,” IEEE International Solid-State Circuits Conference, Feb., 2002.

Multi-hop radio networks

6.1 Introduction

The relay functionality needed in multi-hop radio networks can be provided either by other users terminals – this technique is used in “ad hoc multi-hop networks” – or by fixed installed extension points – this technique is used in “structured multi-hop networks”.

In order to realize the multi-hop wireless network, additional architectural elements and technologies must be considered and implemented in wireless networks, which are described in the following sections.

6.2 Technical aspects of multi-hop techniques

1) Physical layer techniques:

Because of the assumed high channel bandwidth per channel it is assumed that only single frequency repeater techniques come into question. The duplex method used has to provide a high isolation between transmission and reception path of the extension points (EPs) respective relaying terminals. TDD seems to be the best suited duplexing method to cope with the limitations caused by the bandwidth restrictions and the isolation requirements.

2) MAC-layer techniques:

The MAC layer controls the physical layer and establishment/release of transmission paths between mobile terminals, EPs and access points (APs). In particular it controls the duplex method used by the physical layer.

3) Routing:

Routing of data between mobile terminals (MTs), EPs and APs is an essential functionality in multi-hop networks. It has two main functions:

a) selection of routes for the source destination pair (MT-AP via EPs/MTs); and,

b) delivery of messages to their correct destination if a route becomes unavailable without QoS loss.

Different routing techniques can be used to fulfil these functions. They can be classified according to the method of control (centralized or distributed), to the dynamic behaviour (static or adaptive) and to the kind of information they base on (reactive or proactive).

4) Radio resource management:

The radio resource management comprises functions such as handover, power control, congestion control, packet data scheduling, etc. A typical case for terminals in multi-hop radio networks is that the terminal is out of range of a base station. Besides the signalling of control messages over several hops still under control of a base station, a distributed RRM approach seems to be feasible where RRM tasks are managed in a self-organizing manner. Alternatively, an overlay network, e.g. an existing long-range, narrow-band cellular network, might assist in an efficient manner, resulting in a hierarchical network structure. The overlay network can, e.g., determine the frequency band to be used, the amount of time a station is allowed to occupy the allocated frequency, and manage the connection and usage parameter/flow control.

6.3 Architectures of multi-hop wireless network

6.3.1 Ad hoc multi-hop wireless networks

Figure 43

Architecture example of ad hoc multi-hop wireless network

Figure 43 depicts a possible architecture of the ad hoc multi-hop wireless network employing a cellular system and a wireless LAN system as a non-cellular network.

In a conventional network and a current network a wireless terminal is directly connected with a base station. However, in the ad hoc multi-hop network there are also wireless terminals that cannot be connected with a base station because of insufficient receiving level and channel occupation by other terminals. In that case neighbouring terminals relay data traffic of that user terminal to the base station.

6.3.2 Structured multi-hop wireless network

Figure 44

A
rchitecture example of structured multi-hop wireless network
Figure 44 depicts a possible architecture of a structured multi-hop radio network. The employed technology could be a cellular system or a wireless LAN system as a non-cellular network.

Due to the limited coverage of the access points additional extension points are established in the target coverage area. The extension points are either directly or via other extension points and by means of radio links connected to an access point. the extension points possess a relay functionality that allows them to forward data/signals from/to mobile terminals, access points or other extension points. Structured multi-hop radio networks can use for EP-to-EP and EP-to-AP transmission the same radio technology as for MT-to-AP transmission (homogeneous multi-hop network). Alternatively the radio technology for MT-to-AP transmission can be different to those for EP to EP and EP-to-AP transmission.

Since extension points only need a power supply (e.g. solar panels), their installation is easy and cheap. Since extension points are installed in well defined locations and typically with directional antennas, they increase the coverage of an access point in a reliable, predictable way.

6.4 Multi-hop access within cellular system

Current cellular system is based on a direct connection scheme between a cellular terminal and a base station. Once the cellular terminal moves out of the service area (e.g. inside a building or a tunnel), there is no means to communicate with the base station under a current cellular architecture.

(a) in Fig. 43 shows one of the multi-hop access schemes for a wireless network composed in a cellular system. User terminals that have capability of relaying traffic generated from (or destined to) other terminals are used to compose a multi-hopped path between the target user terminal and base station.

In structured multi-hop networks (Fig. 44) the relaying of the traffic is provided by the extension points.

6.4.1 Media access control (MAC)

Cellular terminals (possible relay terminals) within a cell of a base station are controlled by the base station, however, cellular terminals out of the cell cannot receive control packets from the base station, resulting in a dead spot condition. In the multi-hop wireless network the relay terminal or the extension points would control the out of range terminals and deliver traffic to both directions: from the base station to the user terminal and the opposite direction.

In QoS and other performance perspective, wireless terminals including relaying terminals or extension points shall support media access method among appropriate neighbouring terminals/extension points.

6.4.2 User identification

In a conventional cellular network each wireless terminal is distinguished by a unique identifier such as IMSI (international mobile subscriber identity), which is delivered to the network (for example AAA server) at the beginning of a connection setup phase and used for mobility control, accounting and other purposes.

Within the ad hoc multi-hop wireless network relay terminals must deliver such information along with user traffic to the base station and the network. The base station administers user stations along with information of the multi-hopped path and neighbouring terminal toward the user terminal. Alternatively, these kinds of functions can be realized by an existing overlay network.

Within structured multi-hop radio networks the surrounding extension points are permanently known by the access points after an initial set-up phase. The routing mechanism implemented in the access points and extension points selects the appropriate path between mobile terminal and access point.

6.4.3 Handover and routing

When a wireless terminal directly connected with a base station moves out of range, an appropriate handover mechanism would be initiated to maintain a continuous wireless connection. A wireless terminal must select appropriate relaying terminals or extension points and a route toward the base station. For structured multi-hop networks the terminal has just to select the extension point which provides the best link performance. The route is then given inherently by the given network structure. The handover results in a re-routing.

6.5 Multi-hop access within wireless LAN system

In this architecture possible user terminals could be notebook personal computers (PC), personal digital assistant (PDA) and other devices equipped with wireless LAN interfaces.

6.5.1 Media access control (MAC)

As a standard media access control protocol, CSMA/CA (carrier sense multiple access with collision avoidance) scheme can be adopted to the multi-hop system. Other suitable MAC schemes are based on TDMA, either slotted or un-slotted. Each wireless LAN terminal autonomously sends user data. At an access point user data are converted into a wired packet format, and are then delivered to the final destination.

(b) in Fig. 43 shows multi-hop access within wireless LAN system. Current wireless LAN systems do not support multi-hop connections or packet relaying mechanisms, however, an ad hoc connection mode has been achieved for direct connection between two terminals.

6.5.2 User identification

In this architecture a wireless terminal is identified by the MAC address of the wireless LAN interface.

6.6 System interworking among wireless media

(c) and (d) in Fig. 43 show multi-hop connection by interworking among heterogeneous wireless systems in the case of ad hoc multi-hop networks. In this architecture dual mode terminals, for example equipped with a cellular interface and a wireless LAN interface, are used as a gateway to interconnect two systems.

In structured multi-hop networks as shown in Fig. 44 it is possible as well to have extension points that are equipped with both a cellular and a wireless LAN interface. In this case the transmissions between MT and EP and between MT and AP are performed preferably via a cellular interface, whereas the transmissions between EP and AP are preferably performed via a wireless LAN interface. Such an architecture has the advantage of

– lower delay because simultaneous transmissions on the MT-EP and the EP-AP interfaces are possible;

– increased capacity in particular at the MT-EP/AP interface, since the EPs are operated as traffic concentrators.

6.7 Benefits of multi-hop radio networks

Multi-hop technology has advantages, that makes this technology important for enhanced 3G systems and systems beyond 3G. It alleviates, in particular, problems of high data rate cellular radio systems which are basically caused by the high transmission bandwidth and the expected operational frequency bands above 3 GHz.

Advantages are:

• This technology is a means to increase by orders of magnitude the coverage of APs, that is limited because of high path-loss and limited transmission power of MTs, EPs and APs.

• Since EPs can be realized as stand-alone entities (they need only a possibly solar-based power supply) with low infrastructure costs, structured multi-hop radio networks allow very economical coverage and capacity enhancements and permit an economical use of the frequency resources by operators. The usage of relaying terminals instead of EPs avoid the need of additional infrastructure at all. However, the coverage depends in this case on the availability of relaying terminals in the vicinity and on their capabilities. Therefore a combination seems to be useful, where a basic coverage is provided by a structured multi-hop network and relaying terminals may increase the performance in case of high number of wireless terminals.

• Fine and easy to achieve adaptation of the offered traffic capacity per area unit of an AP and the really needed traffic capacity per area unit is possible thereby increasing the spectrum efficiency.

• In case of structured multi-hop radio networks the radio network planning is facilitated. Radio coverage can easily be extended.

• The lower transmission power of the MTs allows longer battery times and lower electromagnetic radiation.

In the multi-hop connection scheme, there shall be two phases, multi-hopped path setup phase and user data transmission phase. In the former phase, multi-hopped path setup sequence and handover sequence that is triggered as a result of movement of user terminal or relaying terminals requires

further investigation. Providing secure connection along the multi-hopped path is another issue to be solved. In a later phase, MAC protocols and relay mechanism that is to be installed on relay terminals are one of the key elements to be further investigated.

6.8 Issues for developing and operating multi-hop systems

Issues to be solved for developing and operating multi-hop systems include the following:

– Relay mechanism

– MAC protocol

– User/terminal authentication and accounting

– Security

– Multi-hopped path setup sequence

– Handover sequence

Further research is needed to reduce the disadvantages of multi-hop networks as e.g. increased delay in case of transmissions via one or more EPs and potential waste of transmission capacity in case of MAC relay. Also the routing within a multi-hop network will be a key challenge.

In general, multi-hop technology can be considered as a useful complement for spectrum sharing, but could be used as well as an alternative to spectrum sharing. Currently advanced concepts – like cooperation between several extension points – are being investigated and promise higher performance.

__________

1 Downstream direction is from base station to mobile station(s); per Recommendation ITU-R M.1399 “Vocabulary of terms for wireless access”.

2 Upstream direction is from mobile station(s) to base station; per Recommendation ITU-R M.1399.

3 “Smart Antennas for Wireless Communications”, Liberti and Rappaport, Wiley, 1999 [9].

4 The United States Federal Communications Commission adopted a First Report and Order, on 14 February 2002, on UWB transmission systems. See In the Matter of Revision of Part 15 of the Commission’s Rules, Regarding Ultra-Wideband Transmission Systems, ET Docket 98-153, First Report and Order, 67 FR 34872, May 16, 2002. The document is available on the Internet at: http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-02-48A1.pdf.

5 The spectral advantages of the MIMO approach are more easily shown by a further grossly over-simplified model:
The capacity limit of a single channel is taken as the classical Shannon expression:

Where SNR is the signal to noise ratio at the receiver for a single channel between two conventional omnidirectional antennas.

If the transmit power is spread equally between M transmit elements and M receive elements are used with conventional phased array beam forming techniques at both ends of the link, then the capacity would approach:

for reasonable SNR.

However, if under similar ideal conditions the power is split over M separate independent channels with the same path loss, then the capacity can approach M times that of each [1,M] link:

for reasonable SNR.

This is of course, a huge over-simplification to illustrate the effect and it assumes that the separated signals from the scattered channels are independent and unaffected by each other.

6The Infostation Challenge: Balancing Cost and Ubiquity in Delivering Wireless Data; Richard Frenkiel, B.R. Badrinath, Joan Boras and Roy Yates, Rutgers University; IEEE Personal Communications, April 2000, Vol. 7 No. 2, page 66.

7 United States Patent No 5,614,914, March 25, 1997, Filed September 6, 1994, Wireless Telephone Distribution System With Time and Space Diversity Transmission for Determining Receiver Location; D. Ridgely Bolgiano and Gilbert LaVean, InterDigital Technology Corporation.

8Anders Furuskar, Sara Mazur, Frank Muller, and Hakan Olofsson; Edge: Enhanced Rates for GSM and TDMA/136 Evolution; IEEE Personal Communications Magazine, Vol. 6 No. 3, June 1999.

9 J. Chuang, X. Qui, and J. Whitehead; Data Throughput Enhancement in Wireless Packet Systems by Improved Link Adaptation with application to the EDGE System; Proc. IEEE VTC ‘99-FALL, Amsterdam, Sept, 1999.

10 United States Patent No 5,859,879, January 12, 1999, Filed August 29, 1997, Wireless Telephone Distribution System With Time and Space Diversity Transmission; D. Ridgely Bolgiano and Gilbert LaVean InterDigital Technology Corporation.

11Mobile Cellular Telecommunications – Analog and Digital Systems; William C. Y. Lee, Air Touch Communications Inc; Second Edition, Publisher McGraw Hill Inc, 1995, Page 563.

12 Optimal Reservation Schedule In Multimedia Cellular Networks, Technical Report, Rutgers University; February 2002; Samrat Ganguly, Badri Nath, Navin Goyal.

13Improvement of IP Packet Throughput with an Adaptive Radio Link Protocol for Infostations’ Technical Report WINLAB-TR-178, April 1999: Hua Mao Wu, James Evans, Michael Caggiano.

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