The air interface of the UMTS Terrestrial Radio Access (UTRA) covers both a frequency division duplex (FDD) part for the paired bands and a time division duplex (TDD) part for the unpaired bands of the UMTS spectrum. Universal Mobile Telecommunication System (UMTS) is the 3rd-generation mobile communication system. This paper presents an interference evaluation of the UTRA TDD. Since both uplink and downlink share the same frequency in TDD, the signals of the two transmission directions can interfere with each other. This interference can occur between two mobile stations or between two base stations within one carrier or between two operators. The interference between uplink and downlink is evaluated by system simulations in this paper. Synchronization and coordination requirements of UTRA TDD are evaluated based on the results.

This paper discusses downlink power control of dedicated channels in UTRA TDD. The current UTRA TDD downlink power control is similar to the one in UTRA FDD mode, that comprises of closed inner loop and quality based outer loop. However, due to the time division feature and associated flexibility with asymmetry of TDD, the inner loop can not operate as fast as in FDD and it is affected by rapid changes in environment. Therefore, the effect of downlii power control of dedicated channel inner loop algorithm to the performance of UTRA TDD network is studied in this paper. A dynamic system level simulator is used for this purpose. 1NTRODUCTlONUTRA TDD that is the TDD (time division duplex) mode of the third generation mobile radio system UTRA (UMTS Terrestrial Radio Access), has been specified in 3GPP (3rd Generation Parmership project) standardization forum [I]. UTRA TDD is intended to operate in the unpaired spectrum of the IMT-2000 band. The UTRA TDD mode uses a combined time division and code division multiple access schemes, and hence the signals of different users are separated both in time and code domain [2]. For spectrum efficient operation, UTRA TDD takes advantage of power control and dynamic channel allocation. Also other radio resource management (RRM) algoritbrns similar to 3G WCDMA system, such as handover, admission control, load control and packet scheduling are utilized. The suitability of the current uplink power control scheme and a 3G WCDMA -type handover algorithm in UTRA TDD network were evaluated in [3], [4] and [5]. In this paper the downlink power control of UTRA TDD is evaluated. The power control algorithm itself, that is based on 3GPP Release 4 standard (3GPP technical specifications, see references [SI, [l I], [12]and [7]), is described and error sources in measurements and signalling are presented. The performance of UTRA TDD network is evaluated by using an advance UTRA TDD system level simulator presented in [3]. The simulator models downlink power control and involved erron in details. UTRA TDD PRINCIPLESThe data modulation scheme in UTRA TDD is QPSK. The modulated data symbols are spread with user specific cbannelisationcodeoflength l...16intheupIinkandl or 16inthe 0-7803-7589-0/02/$17.00 02002 IEEE downlink. The spreading codes of UTRA are based on the Orthogonal Variable Spreading Factor (OVSF) techniques. The use of OVSF allows the spreading factor to be changed and orthogonality between different spreading codes of different lengths to be maintained [2], [IO].The modulated and spread data is then scrambled with a pseudorandom sequence length of 16. Scrambling does not change signal bandwidth but separates terminals or base stations from each other. Pulse shaping filtering is applied to each chip at the receiver so that each chip is filtered with a root raised cosine filter with rolloff factor of a = 0.22 [2], [IO].The frame length of UTRA TDD is IO ms and it is divided into 15 time slots. Duration of each time slot is 666 ps and length 2560 chips. Each of the time slots is alloc...

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This paper discusses downlink inner loop power control of dedicated channels in UTRA TDD. The current UTRA TDD downlink power control is similar to one in UTRA FDD mode, that comprises of closed inner loop and quality based outer loop. However, due to the time division feature and associated fexibility with asymmetry of TDD, the inner loop can not react as fast as in FDD and it is affected by rapid changes in environment. Therefore, the effect of the inner loop algorithm to the performance of UTRA TDD network is studied in this paper. Especially, the use of asymmetric step sizes for "power up" and "power down" commands is evaluated in contrast to the conventional symmetric power adjustment. Since it would be beneficial for the downlink inner loop power control to reach the target SIR as fast as possible, the power control step size based on the difference between the UE measured SIR and target SIR would be the most desirable power adjustment. Since the effectiveness of this type of an algorithm depends on available signaling bandwidth that is used, a study is carried out to find the tradeoff between the signaling bandwidth and related network performance.

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