Differential space-time block-coded OFDMA for frequency-selective fading channels

Combining differential Alamouti space-time block code (DASTBC) with orthogonal frequency-division multiple access (OFDMA), this paper introduces a multiuser/multirate transmission scheme, which allows full-rate and full-diversity noncoherent communications using two transmit antennas over frequency-selective fading channels. Compared with the existing differential space-time coded OFDM designs, our scheme imposes 10 restrictions on signal constellations, and thus can improve the spectral efficiency by exploiting efficient modulation techniques such as QAM, APSK etc. The main principles of our design are s follows: OFDMA eliminates multiuser interference, and converts multiuser environments to single-user ones; Space-time coding achieves performance improvement by exploiting space diversity available with multiple antennas, no matter whether channel state information is known to the receiver. System performance is evaluated both analytically and with simulations

Using Hierarchical Data Mining to Characterize Performance of Wireless System Configurations

This paper presents a statistical framework for assessing wireless systems performance using hierarchical data mining techniques. We consider WCDMA (wideband code division multiple access) systems with two-branch STTD (space time transmit diversity) and 1/2 rate convolutional coding (forward error correction codes). Monte Carlo simulation estimates the bit error probability (BEP) of the system across a wide range of signal-to-noise ratios (SNRs). A performance database of simulation runs is collected over a targeted space of system configurations. This database is then mined to obtain regions of the configuration space that exhibit acceptable average performance. The shape of the mined regions illustrates the joint influence of configuration parameters on system performance. The role of data mining in this application is to provide explainable and statistically valid design conclusions. The research issue is to define statistically meaningful aggregation of data in a manner that permits efficient and effective data mining algorithms. We achieve a good compromise between these goals and help establish the applicability of data mining for characterizing wireless systems performance

OFCDM systems over fading channels

Along with the fast growing demand of information exchange, telecommunication systems are required to provide fast and reliable service to high-data-rate applications such as video conference, real-time broadcasting, and on-line gaming. In downlink transmission, orthogonal frequency and code division multiplexing (OFCDM) has been an attractive technique for high-data-rate applications. With two-dimensional spreading, in both time domain and frequency domain, OFCDM achieves diversity gains in multiuser scenarios. Moreover, the adjustable spreading factors (SF) give OFCDM systems the flexibility in transmission rate and diversity gain. In this thesis, we focus on the downlink of OFCDM communication systems. The performance of OFCDM systems is investigated over Ricean fading channels with Rayleigh fading as special case. Code division multiple access (CDMA) technique is used to support multiuser communications, where users can transmit at the same time using the same frequency with the help of code sequences. We compare different combining methods that are employed to achieve diversity gain. Moreover, channel correlation is examined to see its effect on the system performance. We also propose to combine multiple-input and multiple-output (MIMO) techniques, specifically space-time block coding (STBC), with OFCDM systems. By adding spatial diversity, a MIMO system can provide more reliable transmission compared to a single-input and single-output (SISO) system. The space-time scheme used in our study is Alamouti scheme [1], which employs N = 2 and M antennas at the transmitter side and receiver side respectively. In the thesis, we explain the system structure, transmission and detection methods, and system performance of such MIMO-OFCDM systems. In our study, the expressions of system bit error rate (BER) are considered under the condition that no multi-code interference (MCI) is present. The accuracy of the BER expressions is verified when compared with the simulated ones for both SISO and MIMO-OFCDM systems with different combining methods. These comparisons are carried over different channels and with different system parameters to explore the benefits of OFCDM based systems. Both analytical and simulation results show the large diversity gains achieved when incorporating STBC with OFCDM

Performance of a space-time coded multicarrier CDMA system in frequency-selective Rayleigh channel.

Ph. D. University of KwaZulu-Natal, Durban 2014.The increasing demand for wireless services requires fast and robust broadband wireless communication for efficient utilisation of the scarce electromagnetic spectrum. One of the promising techniques for future wireless communication is the deployment of multi-input multi-output (MIMO) antenna system with orthogonal frequency division multiplexing (OFDM) coupled with multiple-access techniques. The combination of these techniques guarantees a much more reliable and robust transmission over the hostile wireless channel. This thesis investigates the performance of a multi-antenna space-time coded (STC) multi-carrier code-division multiple-access (MC-CDMA) system in a frequency-selective channel using Gold codes as spreading sequences. Spreading codes are known to be central to the performance of spread spectrum systems, STC MC-CDMA systems inclusive. Initial phase of this research work investigates multiple-access performance of spreading codes for the communication system. The performance of different sets of Gold codes for increasing number of interfering users for up to a thousand users and eight different code lengths, ranging from 31 to 4095-chip Gold codes, were considered. Simulation results show that odd-degree Gold codes give better bit-error-rate performance than even-degree Gold codes. Whereas the odd-degree codes exhibited relatively marginal loss in performance when the system was loaded, their even-degree counterparts degraded rapidly in performance, resulting in early emergence of an error floor, culminating in premature system saturation. Furthermore in this thesis, software simulations were carried to investigate the performance of a direct-sequence (DS) CDMA system in a flat-fading Rayleigh channel, and a multi-carrier (MC) CDMA system in a frequency-selective channel using different sets of Gold. The results showed that in a flat-fading channel, the Gold codes provide a constant coding gain close to that obtainable in a Gaussian channel. The results also showed that the impact of longer spreading codes was more pronounced for the MC-CDMA system in a frequency-selective channel as indicated by significant lowering of error floors. Also, frequency diversity associated with the use of longer codes coupled with multi-carrier modulation makes the MC-CDMA system resilient to multi-path effects. Further still, this thesis investigated the performance of a space-time block-coded (STBC) CDMA system in a flat-fading channel. Results showed that at low signal-to-noise ratio, the coding gain provided by the codes surpasses the diversity advantage provided by the use of the multiple antennas. The results also showed that coding gain between no-diversity link and its Gold-coded counterpart is the same as that between the transmit-diversity link and its Gold–coded counterpart. The independence of the diversity advantage provided by multiple transmit antennas and the coding gain obtainable from the use of the spreading sequences enables the prediction of the performance of composite space-time block-coded CDMA systems. Performance of a STBC OFDM system as well as a STBC MC-CDMA system in frequency-selective channel was also investigated. Results showed that the combination of diversity gain from the use of multiple antennas, coupled with coding gain provided by the Gold codes of the CDMA system, plus the diversity gain resulting from frequency diversity of multi-carrier transmission and the spectrum-spreading by the CDMA makes the composite STBC MC-CDMA system resilient to channel fading. This fact is particularly the case for long codes. For example, with reference to the OFDM transmission, the results showed that a 511-chip Gold-coded STC MC-CDMA system provided a factor of about 3,786 reduction in error floor

ANALISIS PERFORMANSI SISTEM WCDMA MENGGUNAKAN MIMO 2x2 PADA KOMUNIKASI ARAH UPLINK (PERFORMANCE ANALYSIS OF WCDMA SYSTEM WITH MIMO 2X2 ON UPLINK COMMUNICATION)

ABSTRAKSI: Teknologi dalam bidang telekomunikasi yang sedang berkembang di Indonesia adalah teknologi 3G. Teknologi 3G menawarkan layanan transfer suara, data, dan video secara realtime bagi penggunanya. Sistem Wideband-CDMA digunakan untuk memenuhi kebutuhan lebar pita frekuensi dan dapat memberikan datarate hingga 2 Mbps. WCDMA adalah teknologi direct spread yang berarti sistem ini akan menyebarkan transmisinya melalui bandwidth dengan lebar 5MHz. Teknologi CDMA (Code Division Multiple Access) memiliki keunggulan dibandingkan dengan teknologi multiple access lainya, seperti TDMA dan FDMA. Tetapi pada sistem ini fenomena multipath fading menjadi masalah yang fundamental. Performansi sinyal akan mengalami degradasi akibat adanya efek multipath fading tersebut. Teknik Multiple Input Multiple Output (MIMO) digunakan untuk mengatasi efek multipath fading. Dengan teknik ini deep fades dapat diatasi dengan replika sinyalnya yang memiliki daya yang lebih kuat, sistem dapat beroperasi pada daya transmit yang rendah, dan juga membuat sistem lebih stabil. Dalam tugas akhir ini menganalisa teknik transmisi Multiple Input Multiple Output (MIMO). Tugas akhir ini akan menunjukan performansi sistem Wideband-CDMA pada arah uplink menggunakan skema STBC (Space Time Block Coding). Teknik deteksi multiuser yang digunakan yaitu decorrelator. Sistem dimodelkan pada kanal propagasi mobile berdistribusi Rayleigh dan AWGN dengan skema antena 2 x 2. Hasil analisa menunjukan bahwa teknik MIMO dapat memeberikan perbaikan performansi pada sistem WCDMA. Perbaikan yang didapatkan sekitar 4 dB pada kecepatan 30 km/jam dengan jumlah user 4. Namum perbaikan akan berubah seiring dengan bertambahnya jumlah user dan kecepatan. Pemakaian decorrelator sebagai pendeteksi multiuser juga memberikan perbaikan performansi pada sistem. Pada kecepatan 30 km/jam dengan 2 user aktif, pemakaian decorrelator memberikan perbaikan sekitar 8 dB. Kesimpulan yang diperoleh, dengan memakai teknik MIMO pada transmitter dan decorrelator pada receiver, akan memberikan hasil yang lebih baik.Kata Kunci : MIMO, WCDMA, decorrelatorABSTRACT: 3G is one of the emerging telecommunication technology in Indonesia. It offers voice, data and video transfer services in realtime to the user. Wideband-CDMA system is used to meet the needs of bandwidth and can provide up to 2 Mbps datarate. WCDMA is a direct spread technology, which means it will spread the transmission over a 5MHz bandwidth. CDMA (Code Division Multiple Access) Technology has advantages over other multiple access technologies such as TDMA and FDMA. But in this system, the phenomenon of multipath fading has become a fundamental problem. Signal will experience a performance degradation due to multipath fading effects. Multiple Input Multiple Output Technique is used to overcome the effects of multipath fading. It can overcome deep fades using the signal replica which has a stronger power, the system can operate at low transmit power, and also makes the system more stable. This final task analize Multiple Input Multiple Output (MIMO) transmission techniques. This final task will show the Wideband-CDMA system performance in uplink using the STBC (Space Time Block Coding) scheme. Decorrelator technique will be used to detect multiuser. The system modeled on the mobile propagation channel with AWGN Rayleigh with 2 x 2 antenna schema. The analysis result shows that MIMO techniques can improve WCDMA system performance. The improvement obtained is approximately 4 dB at a speed of 30 km/h with 4 users. However, the improvement will change with the increasing number of user and speed. The decorrelator as a technique that provides multiuser detection also gives an improvement in the system performance. At the speed of 30 km/h with 2 active users, decorrelator provides approximately 8 dB improvement. So the conclusion is, the result is better with the MIMO technique at the transmitter and the decorrelator at receiver.Keyword: MIMO, WCDMA, decorrelato

ANALISA PERFORMANSI SISTEM WCDMA MENGGUNAKAN MIMO DAN AMC

ABSTRAKSI: Sistem komunikasi celluler saat ini telah memasuki generasi ketiga yang dikenal dengan 3G. Sistem ini menggunakan standar komunikasi wireless wide band code division multiple access (WCDMA). WCDMA adalah teknologi direct spread yang berarti sistem ini akan menyebarkan transmisinya melalui bandwidth dengan lebar 5MHz. Teknologi ini digunakan dalam 3G-UMTS dengan kecepatan data mencapai 2MBps yang dapat melayani pengiriman video, data, gambar untuk layanan mobile internet.Untuk memenuhi layanan data kecepatan tinggi secara realtime dengan performansi yang baik dan mampu bekerja pada kanal multipath fading digunakan teknik MIMO (Multiple Input Multiple Output) sehingga kecepatan data mencapai 20 Mbps. AMC (Adaptive Modulation and Coding) digunakan untuk mendukung transmisi kecepatan beragam untuk tipe yang berbeda dari layanan multimedia. Dalam AMC, level modulasi dan kecepatan coding diatur menurut kondisi kanal.Tugas akhir ini menganalisa dan membandingkan kinerja sistem WCDMA menggunakan MIMO dan AMC yang akan dimodelkan pada kanal propagasi mobile yang berdistribusi Rayleigh Fading. Skema MIMO yang digunakan adalah skema Space Time Block Code 2x2.Hasil analisa menunjukkan bahwa teknik MIMO memberikan perbaikan performansi berkisar antara 0,7 dB sampai 1 dB pada kecepatan rendah (3 km/jam) dan antara 0,7 dB sampai 1,2 dB pada kecepatan menengah (30 km/jam). Sedangkan pada kecepatan tinggi (120 km/jam), MIMO masih belum bisa memberikan perbaikan sistem untuk mencapai target BER 10-3 . Algoritma adaptif modulasi memberikan perbaikan performansi terhadap sistem WCDMA menggunakan MIMO dengan modulasi tetap. Pada kecepatan 3 km/jam, adaptif modulasi memberikan perbaikan berkisar antara 4,3 dB sampai 10,9 dB terhadap setiap jenis modulasi. Sedangkan pada kecepatan 30 km/jam, adaptif modulasi memberikan perbaikan pada BER 10-1 berkisar antara 3 dB sampai 18 dB.Kata Kunci : -ABSTRACT: For now, wireless communication system has come third generation which called 3G. This system use wireless communication standard wide band code division multiple access (WCDMA). WCDMA is direct spread technology, which means that it will spread its transmissions over a wide, 5MHz carrier. WCDMA is the technology used in UMTS, and with data rates up to 2Mbits it has the capacity to easily handle bandwidth-intensive applications such as video, data, and image transmission necessary for mobile internet services.For services high speed data in real time with good performance and can good work in multipath fading channel used MIMO (Multiple Input Multiple Output) technology so data speed up to 20 MBps. AMC is used to support multiple rate transmission for different types of multimedia services. In AMC, the modulation level and coding rate are set by the channel condition.This final task analize and compare performance of WCDMA system with MIMO and AMC that will modelling in mobile propagation channel which distributed Rayleigh Fading. MIMO scheme use Space Time Block Code 2x2The results show that MIMO technology give improvement performance between 0,7 dB until 1 dB in low speed (3 km/hour) and between 0,7 dB until 1,2 dB in medium speed (30 km/hour), MIMO still not give good performance for system to get BER 10-3. Adaptive modulation algorithm gives improvement performance for WCDMA system with MIMO and fixed modulation. In speed 3 km/hour, adaptive modulation give good performance between 0,8 dB until 11,9 dB for every kind of modulation. In the other way, in speed 30 km/hour, adaptive modulation give good performance in BER 10-1 between 3 dB until 18 dB.Keyword:

Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems

Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER

Downlink Steered Space-Time Spreading Assisted Generalised Multicarrier DS-CDMA Using Sphere-Packing-Aided Multilevel Coding

This paper presents a novel generalised Multi-Carrier Direct Sequence Code Division Multiple Access (MC DS-CDMA) system invoking smart antennas for improving the achievable performance in the downlink, as well as employing multi-dimensional Sphere Packing (SP) modulation for increasing the achievable diversity product. In this contribution, the MC DS-CDMA transmitter considered employs multiple Antenna Arrays (AA) and each of the AAs consists of several antenna elements. Furthermore, the proposed system employs both time- and frequency- (TF) domain spreading for extending the achievable capacity, when combined with a novel user-grouping technique for reducing the effects of Multiuser Interference (MUI). Moreover, in order to further enhance the system’s performance, we invoke a MultiLevel Coding (MLC) scheme, whose component codes are determined using the so-called equivalent capacity based constituent-code rate-calculation procedure invoking a 4-dimensional bit-to-SP-symbol mapping scheme. Our results demonstrate an approximately 3.8 dB Eb/N0 gain over an identical throughput scheme dispensing with SP modulation at a BER of 10?5

Area spectral efficiency of soft-decision space–time–frequency shift-keying-aided slow-frequency-hopping multiple access

Slow-frequency-hopping multiple access (SFHMA) can provide inherent frequency diversity and beneficially randomize the effects of cochannel interference. It may also be advantageously combined with our novel space-time–frequency shift keying (STFSK) scheme. The proposed system’s area spectral efficiency is investigated in various cellular frequency reuse structures. Furthermore, it is compared to both classic Gaussian minimum shift keying (GMSK)-aided SFHMA and GMSK-assisted time- division/frequency-division multiple access (TD/FDMA). The more sophisticated third-generation wideband code-division multiple access (WCDMA) and the fourth-generation Long Term Evolution (LTE) systems were also included in our comparisons. We demonstrate that the area spectral efficiency of the STFSK-aided SFHMA system is higher than the GMSK-aided SFHMA and TD/FDMA systems, as well as WCDMA, but it is only 60% of the LTE system