Comp060419.qxd The Journal of Engineering Research Vol. 4, No.1 (2007) 95-102 1. Introduction During the last decade, several standards for Mobile telecommunications have been developed. The most com- mon is the Global System for Mobile Communications (GSM), standardized by the European Telecommunications Standards Institute (ETSI), as a cel- lular communications system operational in many coun- tries around the globe. As GSM depends mainly on Integrated Digital Services Network (ISDN) standard (Rahnema, M., 1993), it is a successful platform for voice calls and data messages. Despite the exceptional features of GSM, it could not be considered as a typical stand for Public safety and Military applications requirements (Tetra Touch, Nokia Tetra Customer Newsletter, 2002; ___________________________________________ *Corresponding author’s e-mail: m.dababneh@surrey.ac.uk Heikonen, K. et al. 2002). Thus, a new brother for GSM is the trunked mobile radio system that is being imple- mented in Europe and is known as, Terrestrial Trunked Radio (TETRA), it is also developed by (ETSI) providing pure digital information technology for the transmission of speech and data. TETRA has been chosen as the plat- form for the operation of nationwide trunked radio net- works in Europe; thus offering efficient and flexible mul- timedia communication services from both Private Mobile Radio (PMR) and Public-Access Mobile Radio (PAMR) users (ETSI, Terrestrial Trunked Radio, 2005). As the cellular mobile communications market experi- ences hot competition, it is essential to compare the per- formance of the competing system types designed for data transmission such as the General Packet Radio System (GPRS) stemming from GSM and others with TETRA to pin point exactly the real usage and applications of the Performance of TETRA and GSM\GPRS as a Platform for Broadband Internet and Multimedia Evolution M. I. Dababneh*1 and E. S. Al-Khawaldeh 1* Department of Electrical Engineering, Alisra University, Jordan Received 19 Apr 2006; accepted 30 September 2006 Abstract: In this paper, a novel approach for the comparison between TETRA system and other contenders is presented showing the relative potentials, thence applications and possible new services. TETRA Voice plus Data (V+D) and GPRS- based-GSM performance are also compared for defined multimedia transmission to revise the capability of both systems to afford multimedia applications to large number of subscribers with the shortest time possible while maintaining the optimal channel utilization. Performance measurements for data transmission illustrate that TETRA exhibits faster time response for connection setup time than the GPRS\GSM applications can provide. Simulation results also confirm that TETRA can sup- port larger number of Mobile Stations (MSs) than the GSM\GPRS for the same time delay period, yet TETRA requires min- imal network resources in comparison with GSM\GPRS for the same supported service. Indeed this is important in the pres- ent time where the demand on wireless communication is increasing dramatically and this what stimulates the concept of this research. Also, the hypothesis that certain communications systems utilizes spectrum efficiency more effectively than others and the fact that radio spectrum is a scarce recourse have further encourages the start of this research. Keywords: TETRA, GSM, GPRS, Call setup-time, Throughput Ωɶf AGOCGGSM/GPRS andRATET.ä’ÉÛG O~©àŸG h á° jô©dG ájOOÎdG á©°ùddG äGP âfÎf’G Qƒ¡¶d √~dGƒÿG .¢S .´ h1@á«æHÉHO .´ .Ω áá°°UUÓÓÿÿGG Ωɶf áfQÉ≤d √ôµàÑeh I~j~L á≤jôW ¢VôY ” ,ábQƒdG √òg ‘ :RATET,áj~÷G äÉe~ÿG á«fɵeGh äÉ≤«Ñ£àdG ¢VôY ”h ɪc á«Ñ°ùædG äGAÉصdG Úæ«Ñe ¬«°ùaÉæeh Ωɶf AGOG áfQÉ≤e ”hRATET Ωɶf ™e 䃰üdGh äÉeƒ∏©ŸG Qƒ¶æe øeGPRSΩɶf ≈∏Y G~ªà©eGSM~jGõàŸG øe~îà°ùŸG O~Y á«£¨àd ᪶f’G á©LGôe ”h Gòg , Ωɶf ¿G í°Vƒj äÉeƒ∏©ŸG åH AG~d ¢SÉ«b .á浇 ájOOôJ IAÉØc ≈∏YG ≈∏Y á¶aÉÙÉHh øµ‡ âbh ô°übÉHRATETΩɶæd ∂dP ™e áfQÉ≤ŸÉH π«°Uƒà∏d ´ô°SG ÜhÉŒ âbh ∂∏Á GPRS Ωɶf ¿CÉH ɪ∏Y ,ÚeɶædG ÚH …hÉ°ùàe ÒNÉàdG âbh ¿G ÚÑJ IÉcÉÙG èFÉàf ∂dòchRATETÉæàbh ‘ G~L º¡e ∂°T ÓH Gòg πbG ᫵ѰT äÉ«fɵeG ¤G êÉàëj øe øµªàæd á浇 á≤jôW π° aCÉH OOÎdG ∫Ó¨à°SG Öéj á«∏Yh Oh~fi Q~°üe äGP äGOOÎdG ¿G ¤G áaÉ°V’ÉH ,᫵∏°SÓdGh ájƒ∏ÿG ä’É°üJ’G ≈∏Y ÒÑc ~jGõJ ∑Éæg ¿G á°UÉNh ô°VÉ◊G .ájƒ∏ÿG ä’É°üJ’G ᪶fG ≈∏Y I~jGõàŸG Ö∏£dG áà«£¨J áá««MMÉÉààØØŸŸGG ääGGOOôôØØŸŸGG ,AÉ£©dG ,áŸÉµŸG ¢ù«°SÉJ âbh :RA, GSM, GPRSTET 96 The Journal of Engineering Research Vol. 4, No.1 (2007) 95-102 various systems depending on the associated characteris- tics, and to explore further services that were not original- ly planned for these systems. Therefore, the aim of this paper is to study TETRA per- formance under the operating mode of V+D. Thus, com- paring it with the GSM\GPRS network regarding the time delay and spectrum channel utilization needed to access the data by the MSs. It is essential however; that the net- work operators supply the subscribers with the required data under demand while maintaining the optimal channel utilization and maximum possible data rate (throughput). This paper starts in Section 2 with an outline of TETRA together with an overview of the GSM\GPRS systems. TETRA network simulation analysis is then presented in Section 3 followed in Section 4 by performance evalua- tion of the GSM\GPRS and complete description of the system. Section 5 describes the relative performance between TETRA and GPRS networks. Finally, the con- clusion section together with a set of recommendations concludes the paper. 2. Overview of TETRA (V+D) and GSM/ GPRS Systems This section introduces the main features for TETRA (V+D) and GSM\GPRS systems. More information about both systems' protocols, signaling and architecture are beyond the subject of this paper and can be obtained from (Rahnema, M., 1993; Tetra Touch, Nokia Tetra Customer Newsletter, 2002; ETSI, Terrestrial Trunked Radio, 2005), and (Bettstetter, C, et al. 1999). 2.1 Overview of TETRA (V+D) System TETRA is a fully digital cellular Private Mobile Radio (PMR) architecture designed for reliable multimedia applications. The main reason to offer the new standard is that the need to provide a standardized network base for Public Safety and Security (PSS) that requires a network capable of support the following five main features detailed in (Tetra Touch, Nokia Tetra Customer Newsletter, 2002; Heikonen, K. et al. 2002): These above requirements are entirely covered by TETRA. However, two modes of operations are defined for TETRA, one of which is the (V+D) mode of operation that allows a unique combination of point-to-point com- munication, point-to-multipoint communication, mobile telephony, and mobile data services accessible from one radio service (ETSI, Terrestrial Trunked Radio, 2005). TETRA assigns uplink and downlink traffic separate- ly. It assigns a user up to four time slots per Time Division Multiple Access (TDMA) frame. When each slot trans- mits at a rate of 7.2 kbps, the four time slots, when com- bined, increases the data rate to 28.8 kbps in an operation known as slot stealing, bandwidth on demand, or multislot operation. This feature makes TETRA an efficient stan- dard for mobile communications having a frequency spec- trum efficiency equivalent to 6.25 kHz per channel per user. Thus, TETRA is considered as a typical platform for data and multimedia applications such as short data mes- sages, status messages and Internet protocol for packet data services. TETRA also supports generic and tailored data applications such as command and control systems, automatic vehicle locations, database queries, reporting, Wireless Access Protocol (WAP) solutions, image trans- fer, and video transmission (Lammerts, E, et al. 1999 and Shearer, E.H.S., 1995). 2.2 Overview of GPRS Based-GSM System A practical extension of GSM is satisfied since 2001 when the service of General Packet Radio System (GPRS) is implemented in Europe and soon around the globe. GPRS is a new service bearer for GSM that greatly improves and simplifies wireless access to packet data networks, e.g., to the Internet. It transfers user data pack- ets in an efficient way between GSM mobile stations and external packet data networks. Packets can be directly routed from the GPRS MSs to packet switched networks. Networks based on the Internet Protocol (IP) and X.25 networks are supported in GPRS (Bettstetter, C, et al. 1999 ). As an improvement over GSM, GPRS supports multi- slot operation, in a similar way used in TETRA, such that each time slot allows data to be transmitted at a rate of 9.05 to 21.8 kbps and up to 171.2 kbps for the total 8 TDMA slots. As in TETRA, GPRS uplink and downlink traffics are allocated separately to provide higher efficien- cy. Under MSs request for transmission, GPRS cell allo- cates physical channels to support GPRS users called Packet Data Channels (PDCH)s where each PDCH con- tains multi logical channels for traffic and signaling (Bettstetter, C, et al. 1999). 3. Performance Evaluation of TETRA 3.1 Performance Criteria and Simulation Model 3.1.1 Call Setup Time For PMR subscribers, one of the most important per- formance criteria is the call setup time. It is essential that a subscriber can request calls and send\download data as fast as possible. This depends critically on the call setup procedure used to access a channel. The frame timing for the call setup procedure considered in TETRA is shown in Fig. 1, which shows the call procedure for two mobile sta- tions; MS A calling MS B via the Base station. The call setup time is defined as the time between the initial access • Group communications, • Average response time in fractions of a second for both individual and group calls, • Seamless radio coverage throughout the whole served area, • Uncomposed and well-recognized high voice quality, • Secure and authenticated connections. 97 The Journal of Engineering Research Vol. 4, No.1 (2007) 95-102 request (U-SETUP message) sent by MS A and the alloca- tion of traffic channel resources (D-CONNECT and D- CONNECT ACKNOWLEDGE messages). However, this call procedure is used for individual (Point-to-Point) calls. The procedure is different in group (Multipoint) call communications where no acknowledge- ment message is required from MS B. Thus, the setup this time can be defined as the time elapsed between the send- ing of the (U-SETUP message) and the transmission of the (D-SETUP message). In both procedures, if the system is loaded, MSs may try several attempts to gain access to the network. This will increase the delay such that the actual delay will equal the sum of the call setup time defined above and the wait- ing time for the MS to gain access to the traffic channel. 3.1.2 Traffic Throughput and Traffic Load Performance Criterias Another important parameter to be considered in the analysis is the traffic throughput. It is defined for control channel during random access as the average number of successful call setups per frame; it is fully simulated in this analysis. The Throughput is affected by the Traffic Load in the network. The Traffic Load is defined as the number of rejected calls per TDMA frame until 95% of the total call requests are succeeded. In other words, the offered traffic is an indication of the number of MSs requesting access to the network resources. As the number of MSs access the net- work increases, the traffic load is increased. Thus, it is expected that call setup time to be enlarged by the increased traffic load. This will become more apparent in Section 3.2. The aim of the simulation study carried out in this sec- tion is to analyze the performance of TETRA network for call setup time delay and the throughput for both individ- ual and group communications. The simulation of TETRA system protocols however, is performed with the follow- ing constraints in place: 3.2 Analysis and Results of TETRA Performance A computer simulation is performed based on the sim- ulation parameters above for both individual (Point to Point) and Group (Multipoint) calls. Figure 2 shows the Complementary Distribution Function (CDF) of percent call success against the Setup time for Point-to-Point calls under different traffic load conditions. The statistical nature of Fig. 2 shows that to reach 95% of call success, an average of 35 TDMA frames (2 seconds) are required for the 0.1 traffic condition (13 suc- cess calls). This value increases to reach 140 TDMA frames (8 seconds) for 0.5 offered traffic (126 success calls). This yields that faster success call rate builds-up when the network exhibits less traffic load. Figure 1. Frame timing of call setup time for TETRA system for point-point calls air interface air interface MS A Base station MS B U-Setup D-Setup D-Cell- Processing U-Connect D-Connect D-Connect Acknowledge • TETRA operates under (V+D) mode of operation • 2500 MSs are uniformly distributed throughout the cell • control channel activity is captured over 10,000 frames • one TDMA frame duration = 56.67 ms • call generation is modeled as Poison process • given the distance between a mobile and the base station, the path loss is calculated as the sum of the average path loss (Hata model) and a 1-path Rayleigh fading channel • the transmission of each message is affected by noise and interference from other mobiles in contention. The statistical behaviour of this interference is assumed similar to additive white Gaussian noise • power control has not been applied • control channel capacity is reserved to support call set-up signaling • it is assumed that sufficient traffic channels are available to support the offered traffic • ALOHA access protocol is applied for uplink and downlink access with a back off time of 3 frames, an access window size of 6, and the maximum number of transmission attempts (if failed) is 5 both uplink and downlink access. Setup Time (No. of Frame) C m m ul at iv e P er ce nt C al l S uc ce ss Figure 2. Set-up time for point-to-point calls 98 The Journal of Engineering Research Vol. 4, No.1 (2007) 95-102 It is clear that, in the case of Group (Multipoint) calls, however, the situation is better. The setup call procedure, discussed in Section 3.1, for Multipoint communications drops the number of messages required to establish a call and this in turn cuts down on loading the control channels hence leaving more capacity for initial random access. Therefore, it is interesting for this research to compare the performance between the Point-to-Point and the Multipoint call procedures by considering Fig. 3. The results presented in Fig. 3 shows that, for the multipoint call procedure setup time measurements, to reach only 95% cumulative, only less than 2 frames are required for the 0.1 traffic (9 success calls) and around 15 frames for 0.5 traffic load (250 success calls). That is there is a drop in setup time for the multipoint call procedure by a large percentage reaching 96% for the same traffic load. Accordingly, much faster call setup times and enhanced TDMA frames utilization are achieved leaving the door open for more MSs to be served more willingly than the situation of Point-Point calls. For this purpose, the Multipoint call procedure is more suitable for group (mul- tipoint) communications applications supported by TETRA. The effect of the offered traffic load on the throughput is graphically depicted in Fig. 4 for Point-to-Point and Multipoint calls. In the case of Point-to-Point calls, it is evident that the throughput increases from 1 to 15 for increasing traffic condition from 0.1 to 0.5. For the same traffic load, then the throughput increases from 10 to 47 in the case of Multipoint calls. As a result, traffic throughput is clearly enhanced in the situation of Multipoint calls. Nevertheless, the throughput performance is degraded for an increasing traffic load for Point-to-Point and Multipoint call procedures. A summa- ry of the above is shown in Table 1. It is obvious from Table 1 that the multipoint call procedure decreases the setup time required to reach 95% success call rate. Taking the 0.5 traffic load condition as a case of study, for the Point-to-Point call procedure, TETRA network rejects 126 MSs from 2506 MSs within 140 TDMA frames giving a throughput of 17 success call per frame. On the other hand, the multipoint call procedure rejects only 14 MSs from 264 MSs requesting access within the setup time of 5.3 TDMA frames, giving a throughput of 47 success calls per TDMA frame. Thus, for such condition of heavy traffic load, the throughput is enhanced by 176%. 4. Performance Evaluation of GPRS-based- GSM 4.1 Performance Criteria and Simulation Parameters GPRS is a service applied over GSM cellular mobile communications which has been established to transmit data in a rate of up to 171.2 kbit/s. The simulation pro- vides analysis for the GSM network based on GPRS serv- ice having two types of data applications; the e-mail and the WWW. The traffic in this case deals with two cases: one with pure WWW and e-mail, and other with mixed WWW and e-mail applications. WWW is based on Hypertext Transfer Protocol (HTTP) layer which manages the transfer of the Hyper Text Markup Language (HTML) documents such as web pages (Shearer, E.H.S., 1997). Each webpage contains a number of objects with certain object size. E-mail depends main- ly on the Simple Mail Transfer Protocol (SMTP) and the Post Office Protocol Version 3 (POP3). HTTP, SMTP and POP3 protocols are located in the application layer but the WWW and email traffic are carried through TCP\IP pro- tocols (Bruce, A. Mah, 1997 and Loshin, P., 2000). GPRS network performance can be measured using the following three main performance criteria's: Setup Time (No. of Frame) C um m ul at iv e Pe rc en t C al l S uc ce ss Figure 3. Set-up time for multipoint calls • Mean Application Response Time : defined as the difference between the time when a user is requesting a web page, or e -mail and the time when it is completely received . • Downlink IP Throughput per user : is the number of IP bits transmitted in each TDMA frame. • Packet Data Channel (PDCH) Utilization : is the number of MAC blocks utilized for MAC data and control data and control blocks normalized to the sum of data, control and idle blocks. Offered Traffic T hr ou gh pu t Figure 4. Throughput for point-to-point and multi- point calls 99 The Journal of Engineering Research Vol. 4, No.1 (2007) 95-102 4.1.1 GPRS Simulation Parameters A computer based simulation is implemented with parameters stated as below: The traffic load parameters of WWW and email are described in Table 2. 4.1.2 GPRS Simulation Environment The Core of the simulator used in this paper is described in Fig. 5. The environment of the simulator is designed to comprise a MS model, a signal generator and a Base Station (BS) receives MS requests through the air interface (Um), a Serving GPRS Support Node (SGSN). All the components are integrated together to feed the sta- tistical evaluation module. 4.2 Analysis and Results of GPRS-based GSM Performance The performance of the GSM network under GPRS service is analyzed using computer simulation for both mixed and pure WWW and e-mail traffic. Figure 6 shows the results for the mean application response time for the case of pure WWW\e-mail traffic. The response time increases from approximately two seconds at low traffic load to 20 seconds for the situation of heavy load. It is clear that WWW exhibits larger time period in compare with that of the e-mail time; as it contains more data. Traffic Load Throughput Setup Time to reach 95% call success [No. of frames] No. of succeeded MSs = No. of success calls No. of rejected MSs = No. of rejected calls Total No. of MSs requesting for access = total number of calls 0.1 1 35 35 2 37 0.2 4 60 240 13 253 0.3 6 88 528 28 556 0.4 13 118.3 1538 81 1619 Point-to- Point 0.5 17 140 2380 126 2506 0.1 10 0.88 9 1 10 0.2 20 1.77 36 2 38 0.3 30 2.65 80 5 85 0.4 40 3.53 142 8 150 Multipoint 0.5 47 5.3 250 14 264 Table 1. Relationship between the traffic load, number of MSs and setup time for point-to-point and multipoint call procedures WWW Parameter Distribution Mean Variance Pages per session Geometric 5.0 20.0 Intervals between pages [s] negative exponential 12.0 144.0 Objects per page Geometric 2.5 3.75 Object size [byte] log2-Erlang-k (k = 17) 3700 1.36 × 106 e-mail Parameter Distribution Mean Variance e-mail size (lower 80 %) [byte] log2-normal 1700 5.5 × 106 e-mail size (upper 20 %) [byte] log2-normal 15700 62.9 × 109 Base quota [byte] Constant 300 0 Table 2. WWW and e-mail traffic parameters • Cluster size (7). • Cell radius = 3000 m. • Velocity of MSs = 6 km/h. • Acknowledged e-mail and WWW applications • Multi-slot capability with one time slot for uplink and four time slots for downlink. • Media Access Control (MAC) protocol is applied. • The e-mail size is (1700 – 15700) byte. • The webpage size is (9250) byte. • 4 Packet data Channels (PDCH) are considered. • 30% of the traffic is assumed to be for e-mails and the rest is assumed to be for the WWW in the case of mixed traffic analysis. 100 The Journal of Engineering Research Vol. 4, No.1 (2007) 95-102 Figure 7 shows the application response time for the mixed WWW\e-mail traffic. As in the case of pure traffic, the response time does increase as the number of active MSs increases, and in this case the time increases from 2 to 7 seconds compared with the case of pure traffic. As a result, the mixed traffic condition greatly speeds up the response time by 80% for heavy load conditions. On the other hand, for the case of pure traffic, the rea- son for the large increase in the response time is apparent from the PDCH utilization measurements shown in Fig. 8 where in, approximately 100% utilization is reached when 15 MSs are competing to use the available PDCH chan- nels. In Fig. 9 however, the PDCH utilization seems to have linear relationship with the number of MSs. Therefore, instead of 100% utilization attained for pure traffic to serve 15 MSs, the mixed traffic decreases the PDCH uti- lization down to 70% for 20 MSs. Thus, the mixed traffic condition saves 30% of the available PDCHs and enables more MSs to access channel resources, thus resulting in better spectrum utilization. Figure 10 shows graphically the measurements of the mean downlink IP throughput per user during transmis- sion periods. It would be appropriate to discuss Fig. 10 and Fig. 8 of PDCH utilization together. The situation of 2 MSs illustrates that the network can offer high data rate (around 22kbit\s) while utilizing 20% of the available PDCHs. As expected, the situation becomes poorer once Figure 5. GRPS simulation environment WWW e-mail Number of MS 0 5 10 15 20 30 25 20 15 10 5 0 M ea n A pp lic at io n R es po ns e Ti m e (s ) Figure 6. Mean application response time for pure WWW\e-mail traffic 0 5 10 15 20 Number of MS 30 25 20 15 10 5 0 M ea n A pp lic at io n R es po ns e Ti m e (s ) Figure 7. Mean application response time for mixed WWW\e-mail traffic WWW e-mail 101 The Journal of Engineering Research Vol. 4, No.1 (2007) 95-102 the network is loaded by 15 MSs, in which the data rate is truncated down to be less than 5kbit/s and the PDCHs uti- lization is in excess of 80%. The throughput measurements seen in Fig. 11, indicates that its rate of decrease is slower than the case of pure traf- fic analysis shown in Fig. 10. Therefore, it is evident that the throughput decreases as the number of MSs increases, but this time from approximately 20kbit/s down to 10kbit/s rather than 5kbit/s for pure traffic. Though, at heavy traffic load, the mixed traffic condition increases the downlink throughput data rate by approximately 100%. Furthermore, and for the case mixed traffic condition, the enhanced performance in the response time and throughput are due to the fact that better PDCH channel utilization is applicable for mixed traffic situation. This is obvious from Fig. 8 in comparison with Fig. 10. Finally, comparing e-mail application with WWW application yields that the e-mails exhibits shorter applica- tion response time than the WWW. This comes from the fact that WWW web pages contain more data than the e- mails. This shows that WWW application has poorer PDCH utilization and throughput performance. 5. Relative Performance between TETRA and GSM\GPRS An assessment for the study of TETRA and GSM/GPRS networks is provided in this section. Also, Simulation models for TETRA and GPRS networks under defined conditions have been implemented. The relative performance criteria measurements for both network types are compared together. The setup time delay for the TETRA (V+D) network is compared to the WWW\e-mail response time for the GPRS network. The relationship between the time delay measurements of both the throughput and the number of MSs is also discussed and fully analyzed. 5.1 Setup Time in TETRA versus Application Response Time in GPRS A summary of the setup time delay in TETRA and the 0 5 10 15 100 80 60 40 20 0 Number of MS D ow nl in k PD C H % u til iz at io n Figure 8. Mean downlink PDCH utilization for pure WWW\e-mail traffic WWW e-mail WWW e-mail 0 5 10 15 20 Number of MS 100 80 60 40 20 0 Figure 9. Mean downlink PDCH utilization for mixed WWW\e-mail traffic 0 5 10 15 20 Number of MS 25 20 15 10 5 0 M ea n do w nl in k IP th ro ug hp ut p er u se r [k b it/ s] WWW e-mail M ea n do w nl in k IP th ro ug hp ut p er u se r [k b it/ s] Figure 10. Mean downlink IP throughput for user per pure www\e-mail traffic 0 5 10 15 20 WWW e-mail Number of MS 25 20 15 10 5 0M ea n do w nl in k IP th ro ug hp ut p er u se r [k bi t/s ] Figure 11. Mean downlink IP throughput for mixed WWW\e-mail traffic 102 The Journal of Engineering Research Vol. 4, No.1 (2007) 95-102 application response time in GPRS is provided in Table 3. Time delay measurements shown are chosen for different traffic load conditions. The e-mail traffic load condition is chosen as it consumes less response time than the WWW application. As a sample of measurements, to serve around 250 MSs, TETRA needs around (3.4 s) and (300 ms) for Point-to-Point and Multipoint call procedures respectively. On the other hand, the GPRS network serves 18 MSs during (30 s) and (5 s) for pure and mixed traffic respectively. It is apparent therefore that TETRA, in com- parison to GPRS, serves much larger number of MSs for the same time duration and this results in shorter delay time. The assessment of the two networks can not be com- pleted until the throughput evaluation is revised with its relationship to the traffic load, time delay measurements as well as channel utilization. 5.1.1 Throughput versus the number of MSs in TETRA and GPRS The definition of throughput performance criteria dif- fers between TETRA and GPRS networks. In TETRA it is defined for control channel during random access as the average number of successful call setups per TDMA frame. In GPRS however, it is defined for the downlink IP packets; as the number of bits transmitted per TDMA frame per user. In general, the throughput is an indication of the data rate of transmission or the speed of access and it is relat- ed to the number of MSs (traffic load) in the network. To cope with the definition of the traffic throughput, defined in Section 3.1 for TETRA network; as the average number of MSs per total application response time is cal- culated in the GPRS network. procedures in TETRA sup- port higher capacity for the offered traffic load. This is a manifest that TETRA strongly supports high capacity traf- fic and group calls suitable for PSS requirements. The results of this comparison are shown in Figure 12 for TETRA network and in Fig. 13 for GPRS network. In Fig. 12, note that the throughput definition for TETRA network is measured per one second rather than per TDMA frame. As a summary, Fig. 11 shows the measurements of the number of success calls per second, whereas Fig. 13 meas- ures the number of completed applications per one sec- ond. Therefore, it is clear that multipoint call procedure enhances the capacity for the random offered traffic com- pared to the Point-to-Point call procedure. In comparison to GPRS, It is evident that both call procedures in TETRA support higher capacity for the offered traffic load. This is a manifest that TETRA strongly supports high capacity traffic and group calls suitable for PSS requirements. 6. Conclusions It is obvious from the simulation analysis that the GSM\GPRS network performance degrades as the num- ber of MSs is increased with limited number of PDCH channels. The mixed traffic condition shows superior per- formance relative to pure WWW and e-mail applications in the response time, IP throughput, and PDCH Utilization performance criterias. Thence, under heavy loaded net- work situations and mixed traffic condition the GSM\GPRS network saves approximately 30% of the available PDCHs, increases the data rate by around 100% and deceases the response time by approximately 80%. The comparison between the results obtained from the GSM\GPRS network and the TETRA network states that TETRA performance is better in both: time delay and the number of mobile stations in the network. This leads to assert that TETRA strongly supports multimedia applica- tions compared to GSM\GPRS network for the same time delay conditions. In accordance with the lower number of control mes- sages needed in the call procedure, it is found that TETRA call setup time for voice and data traffic in the case of group communications procedure is faster than in the case of individual calls. Furthermore, the throughput perform- ance criterion for group call procedure enhances the net- work performance by 176% for the case of heavy traffic load of 0.5, thence leave more traffic channels idle for ran- dom access. Comparing the throughput measurements for both net- work types shows that, network performance degrades as traffic load in the network increases. References Bettstetter, C. Vögel, H. and Eberspacher, J., 1999, "Gsm Phase 2+ General Packet Radio Service Gprs: Architecture, Protocols, And Air Interface," IEEE Communications Surveys, http://www.comsoc.org/pubs/surveys, Vol. 2(3). Bruce, A. Mah., 1997, "An Empirical Model of HTTP Network Traffic," Infocom, pp. 592, INFOCOM. ETSI, 2005, "Terrestrial Trunked Radio (TETRA) Voice Plus Data (V+D). Part1, General Network Design; Final Draft," EN 300.3921 Vol..3.0. Heikonen, K. and Saaristo, T., 2002, "You and Your TETRA RADIO, TETRA as a Tool for Public Safety," IT Press Edita Publishing Ltd. Lammerts, E. Slump, C. H. et a., 1999, "Realization of a Mobile Data Application in TETRA," STW, 10 19- 01:038. Loshin, P., 2000, "Essential Email Standards; RFCs and Protocols Made Practical," John Wiley & Sons. Rahnema, M., 1993, "Overview of the GSM System and Protocol Architecture," Communication Magazine, IEEE Vol. 31(4), pp. 92-100. ISSN 0163-6804. Shearer, E.H.S., 1995, "TETRA - A Platform of Multimedia," Philips Telecom - PMR Cambridge. "TETRA Touch, 2002, Nokia TETRA customer newslet- ter" www.nokia.com/tetra, Vol. 2.