Performance of low complexity turbo-codes in the UTRA-TDD-mode

The acquisition problem in the wideband-CDMA (WCDMA) system proposed by the 3rd Generation Partnership Project (3GPP) to the ITU consists of determining both the timing and the identity of the particular scrambling code being received. A fast search mechanism to tackle this problem, based on cyclically permutable (CP) codes is proposed by Sriram and Hosur (see IEEE Inter. Conf. on Communications (ICC), June 1999) for the frequency-division-duplex (FDD) component of WCDMA. The CP codes for the FDD mode of WCDMA are not optimum for the time-division duplex (TDD) mode and have to be redesigned. In this paper we design optimum CP codes for the TDD mode. The new CP codes can also identify both frame timing and long code group information using only one synchronization slot. Thus, they can be used for GSM to WCDMA TDD mode handover. The new CP codes have been incorporated into the 3GPP WCDMA TDD standard.

In this paper, a comparison study of various UMTS data transmission techniques is performed. An analysis of the system in the presence of geographically non-uniform multi-service traffic profiles is done for three transmission techniques: Frequency Division Duplex (FDD), Time Division Duplex (TDD), and High Speed Downlink Packet Access (HSDPA). Several combinations were selected: FDD, TDD, FDD combined with HSDPA, FDD combined with TDD, and FDD combined with TDD and HSDPA. The TDD mode is the technique with better results, but the introduction of HSDPA is clearly beneficial for data services, as expected. The distribution of the services by the three techniques is the best scenario, namely for some traffic profiles. For example, for a threshold of 128 kbps (for HSDPA services) and 50 % of the power reserved to HSDPA, it is possible to get 1.4 GB of carried traffic.

Massive MIMO has been proposed as a means of achieving huge spectral efficiency in cellular networks. However, its implementation is usually based on linear precoding schemes using Channel State Information (CSI). For this reason, the use of the Time Division Duplex (TDD) mode is typically assumed since it removes the dependence on the number of antennas at the transmitter to acquire CSI. Unfortunately, most of the cellular network operate in the Frequency Division Duplex (FDD) mode in which the acquisition of CSI depends proportionally to the number of transmit antennas. For this reason, the implementation of Massive MIMO is handicapped to few transmit antennas for the current cellular networks. In this paper we study the use of reconfigurable antennas that can switch among a set of preset modes, i.e., radiation patterns, through Blind Interference Alignment schemes. We show that it is a solution to exploit a very large number of antennas at the transmit side, overcoming the bottleneck that today constitutes the acquisition of CSI in Massive MIMO systems operating in FDD mode.

This paper reports on the application of SAW filters in the Universal Mobile Telecommunications System (UMTS), the new third generation mobile communication system. A brief system overview of the UMTS Terrestrial Radio Access (UTRA) physical layer standardized by the European Telecommunications Standards Institute (ETSI) will be presented. System simulations of a UMTS transceiver designed for commercial use are discussed. SAW filters are applied in both the transmit and receive path of the RF and IF parts. The correlations between filter characteristics, like group delay ripple, effective magnitude and phase errors, and system characteristics, such as Error Vector Magnitude (EVM), are evaluated. Such kind of system simulations covers not only the system design itself but also governs the design of SAW filters since it accounts for the special influence of the SAW RF and IF filter characteristics on the UMTS system performance.

In the universal mobile telephony system (UMTS) the frequency division duplex (FDD) and time division duplex (TDD) modes have adjacent carriers at 1920 MHz. This creates adjacent channel interference (ACI) between the two different air interfaces. Since different duplexing modes are used, the implications for each system are different, with respect to capacity and coverage: these implications are investigated in the paper. The separation distance of the TDD and FDD base station and the load in each system are varied and a symmetrical speech service in both systems is considered, with non-ideal power control assumed. It is found that for an FDD cell radius of 1000 m, a TDD cell radius of 50 m and 10% maximal tolerable outage, the effects of ACI on capacity can be compensated by dynamically increasing the required power at each BS, without affecting the coverage.

In the 3/sup rd/ Generation Partnership Project (3GPP) time division CDMA (TD-CDMA) has been selected as the air interface for the TDD (time division duplexing) bands of 3/sup rd/ generation (3G) mobile radio systems. In this paper a novel multiuser transmission scheme for the TD-CDMA downlink is presented which in contrast to state of the art TD-CDMA transceivers utilizes the reciprocity of the mobile radio channels of the uplink and the downlink. It is shown that according to this scheme no channel estimation is necessary at the MSs and the data detection effort is dramatically reduced. The theoretical analysis of the paper is supported by computer simulation results which illustrate the superiority of the novel scheme in terms of the BER (bit error rate) performance and the system spectrum efficiency in the downlink of TD-CDMA.

The 3GPP proposal for 3rd generation mobile phone systems comprises not only frequency division duplex (FDD) but also time division duplex (TDD) as duplex method for the JD-CDMA system. The TDD mode is an addition to the FDD mode to facilitate flexible, asymmetric data transfer of up- and downlink. Special structured pilot sequences are included into the data bursts and can be exploited to perform an efficient joint channel estimation of all active users as basis for multiuser detection. In this paper linear receiver concepts for the TDD mode are examined in terms of performance with focus on the influence of real, non-ideal channel estimation. RAKE receiver, zero forcing and minimum mean-square-error multiuser detectors are introduced and investigated by means of simulation for different environments using appropriate ITU channel models. Furthermore, an improved channel estimation procedure is presented, yielding significant performance enhancements for the multiuser detection algorithms.

The potential of combining channel pre-equalization with transmit diversity for orthogonal frequency-division multiple-access code-division multiplexing (OFDMA-CDM) systems is investigated. The pre-equalization exploits the channel knowledge which is presumed to be available at the transmitter (Tx). The transmission signal is pre-distorted according to the channel state information (CSI) which can be made available, for example, by using time division duplex (TDD) mode. In TDD mode and under the assumption that CSI changes slowly in time, CSI estimated from a received slot can be used for pre-equalization of the next transmission slot. Concerning transmit diversity, we consider space-frequency block coding (SFBC) and transmit selection diversity (TSD). It turns out that TSD significantly outperforms SFBC. Moreover, systems with pre-equalization and TSD exhibit lower complexity than systems with pre-equalization and SFBC, since in the former case CSI is needed only at Tx, while in the latter case CSI is required at both Tx and receiver (Rx). In addition, it is shown that TSD is the optimal transmit diversity technique in the sense of bit error rate (BER) minimization in the case when CSI is available at Tx.

The Universal Mobile Telecommunications System (UMTS) is a third generation mobile system, which is expected to be launched within the next 10 years. It is expected to offer global coverage (by using the universal personal standard), services up to multimedia, and air interface bit rates up to 2 Mbps through all personal, business and residential modes. Therefore, UMTS is expected to be an integration of mobile and fixed networks by using hierarchical layered cell structures. There are many research programmes that are focussing on UMTS and the possible scenarios of its implementation. One of them is the Advanced Communications Technologies and Services (ACTS), which is the successor of RACE. UMTS has to be economic viable and 'future-proof' to be able to support forthcoming services. Hence, any possible launch schemes have to take into account the fact that some particular second generation systems have proved to be very popular and constitute serious investments. For these reasons, they cannot be discarded. An analytical review of the most important existing candidate schemes are presented.

A throughput analysis of ARQ Types I and based on simulations for unconstrained delay data (UDD) services is presented. We emphasise differences between Types I and II and consider Types II and III as minor variants of the same scheme which we call II-III for the purpose at hand. For this contribution, a subset of the protocol on Layers 1-3 for UMTS terrestrial radio access (UTRA) time division duplex (TDD) mode is simulated for a single cell. Both user traffic and signalling messages suffer from path-loss, fading, and interference in the model. Interference due to traffic in neighbouring cells is also taken in to account through the actual value interface. Results are obtained for downlink traffic for various code-rates and interleaving schemes. The available results include capacity, signalling overhead, the distribution of the number of retransmissions, and PDU delay. It is shown that Type greatly outperforms Type I for the cases 2048 Pico and 384 Micro in terms of capacity and the number of retransmissions. Although, the benefit of using Type over Type I becomes smaller at lower bit rates it is still significant. This is exemplified by simulation results for the case 8 Micro. We conclude that Hybrid ARQ Type outperforms Type I for all UDD services between 8 kb/s and 2 Mb/s for UTRA TDD mode.

Multi-user multiple-input multiple-output (MU-MIMO) system operating in frequency division duplex (FDD) mode has an advantage over that operating in time division duplex (TDD) mode in achieving a lower return time latency as both the uplink and downlink data streaming can occur simultaneously. However, unlike TDD, the reciprocity of the uplink and downlink channels does not hold and hence the system typically needs to rely on channel feedback which reduces the uplink channel capacity. Reducing the channel feedback while maintaining the channel estimation accuracy is a critical factor for a successful implementation of MU-MIMO FDD. In addition, when combined with orthogonal frequency division multiple access (OFDMA), channel feedback needs to occur independently for different sub-channels assigned to different user terminals. This paper proposes the use of discrete cosine transformation (DCT) based channel compression for the purpose of MU-MIMO-OFDMA channel feedback and shows its advantage over conventional discrete Fourier transform (DFT) based method. Compared to ideal channel feedback without channel estimation or compression errors, the proposed method achieves within 1 dB loss in uncoded bit error performance for a MU-MIMO-OFDMA system using 32 antennas at the central access point supporting 16 user terminals each with a single antenna.

The continuous growth in mobile data traffic and limited license wireless spectrum have led to dramatically increase the demand of the radio spectrum. It is widespread the concern about the coexistence of long term evolution (LTE) and Wi-Fi in the unlicensed band. There are several techniques have been proposed to enable the coexistence of LTE and Wi-Fi in the unlicensed band, but these works are targeted on the impact of the LTE to the Wi-Fi network performance. An experiment is carried out in this work to evaluate the impact of Wi-Fi signal on the video streaming in the LTE network. The experimental test comprised of the national instrument (NI) universal software radio peripheral (USRP) 2953R that is controlled by the LabVIEW Communication LTE application framework. Extensiveexperiments are carried out under two scenarios, i.e. (1) Coexistence of LTE and Wi-Fi signal, (2) LTE signal only. Performance evaluations are carried out with different Modulation and coding schemes (MCS) values and different mode of operations, i.e. frequency division duplex (FDD) and time division duplex (TDD) mode. The results illustrated that the interference from Wi-Fi signal caused the performance degradation of the LTE network in throughput and the power received by user equipment (UE).

A reconfigurable digital root raised cosine (RRC) filter for a UMTS terrestrial radio access (UTRA) mobile terminal receiver is implemented on a Xilinx Vitrex II Pro Field Programmable Gate Array (FPGA). The filter employs a finite impulse response (FIR) and monitors in-band and out-of-band received signal powers and calculates the appropriate filter length that meets the bit-energy to interference ratio (Eb/No) of the system. The results presented are for the time division duplex (TDD) mode of UTRA.

The authors examine the time-division duplex (TDD) mode of code-division multiple access (CDMA) communications. The differences from frequency-division duplex (FDD) are shown, and the advantages of using a TDD system are discussed. The TDD mode facilitates the implementation of several functions in the areas of power control, RAKE combining, and selection diversity combining, which can reduce the complexity of mobile units and improve system capacity.

The advanced knowledge of forward link channel information enables the optimal transmit waveform to be designed for a multiple input multiple output (MIMO) antenna system to exploit the channel's characteristics fully. The reciprocal property of the radio channel makes time division duplex (TDD) an attractive air interface design since the forward link channel information can be derived from the reverse link signal without any explicit feedback. Among the many practical factors that may invalidate the channel reciprocity in TDD mode, this paper focuses on those that are associated with the mismatches among the radio frequency (RF) circuits in the many transmit/receive chains. With a simple model, the sources for the RF mismatches are identified and their calibration requirements are established using simulation.