Enabling Broadband Wireless Technologies

This paper proposes a transmission diversity (TD) technique combined with orthogonal frequency division multiplex (OFDM) modulation to enhance packet-error-rate (PER) performance in microcell broadband wireless communication systems. The proposed TD technique selects the antenna with the anticipated better-channel conditions in a subchannel-by-subchannel manner at the access point (AP) based on the quality-measurement results of signals sent by the mobile terminal (MT). In the subsequent transmission timing from the AP to the MT, each antenna at the AP station transmits OFDM-modulated signals that only possess the selected subchannel components. On the MT side, the space-combined whole subchannel OFDM signal is received through the single antenna.

The convergence of high data rate multimedia services such as speech, audio, video, image and data will be the main features of future wireless systems. Multi-carrier code division multiple access (MC-CDMA) is one of the powerful techniques to meet the requirements of next generation broadband and wireless mobile communication systems. MC-CDMA system allows many users to get the benefit of both orthogonal frequency division multiplexing (OFDM) technique and code division multiple access scheme (CDMA). It offers high spectral efficiency, high data rate, low transmit power, lower implementation complexity, large system capacity and narrowband interference rejection capability. Multicarrier systems are very sensitive to carrier frequency offset (CFO) caused by Doppler shifts and imperfections of transmitter and receiver oscillators, which leads to loss of orthogonality among the subcarriers resulting in intercarrier interference (ICI). In this paper, a low complexity receiver phase rotated conjugate cancellation (RPRCC) algorithm using an iterative maximum likelihood (ML) based CFO estimation is proposed. The proposed method reduces the ICI which in turn reduces the multiple access interference (MAI) and subsequently increases the system capacity. Simulation results show that the RPRCC method provides better carrier to interference ratio (CIR) and bit error rate (BER) performance compared to transmitter phase rotated conjugate cancellation (PRCC) technique and conventional conjugate cancellation (CC) scheme.

The huge demand and growth of high-speed mobile data applications drive the development of the next generation wireless systems. The emerging 3G cellular networks provide new wireless access technologies for high-speed downlink packet access. The variable nature of wireless channel quality brings up challenges and opportunities for wireless system design. By utilizing channel state information, the next generation wireless packet systems provide high data rate communications with adaptive modulation and coding. To provide quality of service (QoS) in such systems is an important engineering issue. In this paper, we propose a novel scheduling algorithm that supports assured QoS. Due to the unpredictability and volatility of wireless medium, wireless QoS design tends to focus on soft QoS guarantee instead of hard one. The proposed scheme can effectively guarantee soft rate reservation and provide high-speed connections with channel-aware radio resource allocation without compromising fairness.

IEEE 802.16/WiMAX-based broadband and mobile wireless access is expected to be a significant component in the next generation (e.g., beyond 3G, 4G) wireless systems. IEEE 802.16/WiMAX standard, which incorporates several advanced radio transmission technologies such as orthogonal-frequency division multiplexing (OFDM), adaptive modulation and coding, and adaptive forward error correction (FEC), is designed to provide broadband wireless capability using a well-defined quality-of-service (QoS) framework. Therefore, this is a promising technology for wireless services requiring high- rate transmission (in the range of tens of Mbps) and strict QoS requirements in both indoor and outdoor environments. This technology is currently of big interest to researchers and practitioners involved in the design, analysis, installation, and management of mobile broadband wireless access systems and networks. The objective of this tutorial is to provide a complete overview on the IEEE 802.16/WiMAX standard and the current state-of-the-art research on the design, analysis, and optimization of IEEE802.16/WiMAX-based networks. The key technical challenges related to protocol engineering in these networks are described. The aim is to provide a survey on the emerging IEEE 802.16/WiMAX technology rather than an in-depth study on a specific protocol engineering problem. An overview of the different evolutions of the IEEE 802.16/WiMAX standard broadband wireless access (BWA) is presented and the open research issues in protocol engineering (e.g., for radio resource management, mobility support, security) are identified. A comprehensive survey on radio resource management, traffic scheduling, admission control, mobility management, and security mechanisms for IEEE 802.16/WiMAX are provided. A comparative performance study among the third-generation (3G) and the IEEE 802.16-based systems is provided. Several applications (e.g., wireless telemedicine and e-health services), services and deployment scenarios are described and the necessary protocol design and engineering issues are outlined.

Coverage study for broadband wireless systems using link adaptation and diversity combining techniques

OFDM (Orthogonal Frequency Division Multiplexing) is a well-known multicarrier modulation technique that allows high-rate data transmissions over multipath broadband wireless channels. By usingOFDM, a high-rate data stream is split into a number of lower-rate streams that are simultaneously transmitted on different orthogonal subcarriers. Thus, the broadband channel is decomposed into a set of parallel frequency-flat subchannels; each one corresponding to an OFDM subcarrier. In a single user scenario, if the channel state is known at the transmitter, the system performance can be enhanced by adapting the power and data rates over each subcarrier. For example, the transmitter can allocate more transmit power and higher data rates to the subcarriers with better channels. By doing this, the total throughput can be significantly increased. In a multiuser scenario, different subcarriers can be allocated to different users, which constitutes an orthogonal multiple access method known as OFDMA (Orthogonal Frequency Division Multiple Access). OFDMA is one of the principal multiple access schemes for broadband wireless multiuser systems. It has being proposed for use in several broadband multiuser wireless standards like IEEE 802.20 (MBWA: http://grouper.ieee.org/groups/802/20/), IEEE 802.16 (WiMAX: http://www.ieee802.org/16/, 2011) and 3GPP-LTE (http://www.3gpp.org/). This chapter focuses on the OFDMA broadcast channel (also known as downlink channel), since this is typically where high data rates and reliability is needed in broadband wireless multiuser systems. In OFDMA downlink transmission, each subchannel is assigned to one user at most, allowing simultaneous orthogonal transmission to several users. Once a subchannel is assigned to a user, the transmitter allocates a fraction of the total available power as well as a modulation and coding (data rate). If the channel state is known at the transmitter, the system performance can be significantly enhanced by allocating the available resources (subchannels, transmit power and data rates) intelligently according to the users’ channels. The allocation of these resources determines the quality of service (QoS) provided by the system to each user. Since different users experience different channels, this scheme does not only exploit the frequency diversity of the channel, but also the inherent multiuser diversity of the system. In multiuser transmission schemes, like OFDMA, the information-theoretic system performance is usually characterized by the capacity region. It is defined as the set of rates 6

Spectral efficiency of a communication system refers to the information rate that the system can transmit reliably over the available bandwidth (spectrum) of the communication channel. Enhancing the spectral efficiency is without doubt a major objective for the designers of next generation wireless systems. It is evident that the telecommunications industry is rapidly growing due to the high demands for ubiquitous connectivity and the popularity of high data rate multimedia services. As well-known, wireless channels are characterized by temporal and spectral fluctuations due to physical phenomena such as fading and shadowing. A well-established approach to exploit the variations of the fading channel is opportunistic communication, which means transmitting at high rates when the channel is good and at low rates or not at all when the channel is poor. Furthermore, in the last few years, the research focus has turned into exploiting the broadcast nature of the wireless medium and the potential gains of exploiting the interaction (cooperation) between neighboring nodes in order to enhance the overall capacity of the network. Cooperative communication will be one of the major milestones in the next decade for the emerging fourth and fifth generation wireless systems. Cooperative communication can take several forms such as relaying the information transmitted by other nodes, coordinated multi-point transmission and reception techniques, combining several information flows together using network coding in order to exploit side information available at the receiving nodes, and interference management in dense small cell networks and cognitive radio systems to magnify the useful information transmission rates. We propose to exploit all sources of capacity gains jointly. We want to benefit from old, yet powerful, and new transmission techniques. Specifically, we want to examine optimal resource allocation and multiuser scheduling in the context of the emerging network architectures that involve relaying, network coding and interference handling techniques. We like to call this theme opportunistic cooperative communication. With the aid of opportunistic cooperative communication we can jointly exploit many sources of capacity gains such as multiuser diversity, multihop diversity, the broadcast nature of the wireless medium and the side-information at the nodes. We suggest exploring opportunistic cooperative communication as the choice for future digital communications and networking. In this direction, we introduce the topic of buffer-aided relaying as an important enabling technology for opportunistic cooperative communication. The use of buffering at the relay nodes enables storing the received messages temporarily before forwarding them to the destined receivers. Therefore, buffer-aided relaying is a prerequisite in order to apply dynamic opportunistic scheduling in order to exploit the channel diversity and obtain considerable throughput gains. Furthermore, these capacity gains can be integrated with other valuable sources of capacity gains that can be obtained using, e.g., multiuser scheduling, network coding over bidirectional relays, and interference management and primary-secondary cooperation in overlay cognitive radios systems. The gains in the achievable spectral efficiency are valuable and hence they should be considered for practical implementation in next generation broadband wireless systems. Furthermore, this topic can be further exploited in other scenarios and applications.

In broadband wireless communication systems. The multipath channel has a significant impact on system design and performance. The polarization diversity antenna is one approach to mitigate the detrimental fading caused by the multipath phenomenon. Thus, antenna design is an important aspect and the development of economical mm-waves equipment that is compact and lightweight is one of the key issues. This paper therefore explores areas of strategic importance in integration of new antenna topology, which are appropriated for use as a building block for the wireless system. The technique proposed here consists in the design of a new configuration of planar antenna led by electromagnetically coupled CPW on single layer substrate for exciting dual polarizations. This antenna configuration is bused on a cross-slot coupling a patch antenna. A rectangular microstrip patch is placed one side of the substrate while a cross-slot fed by a coplanar line is arranged opposite to the patch in the ground plane on the other side of the substrate. The antenna is designed on a high dielectric constant substrate (/spl epsiv/r=9.9), which is close to the dielectric constant of GaAs around 35 GHz and demonstrates the feasibility of integration of such an antenna structure into monolithic circuits.

The Long Term Evolution (LTE) standards are generated by the Third Generation Partnership Project (3GPP) for the Fourth Generation (4G) wireless communication systems. The Fourth Generation (4G) wireless communication standards use new physical layer signaling techniques in their physical layer. Single Carrier Frequency Division Multiple Access (SC-FDMA) and Orthogonal Frequency Division Multiple Access (OFDMA) are the two major signaling techniques used in LTE. OFDMA is used in the downlink of the Fourth Generation (4G) wireless communication systems for its high spectral efficiency and SC-FDMA is used in the uplink of the Fourth Generation (4G) wireless communication systems for its high power efficiency. The main objective of this paper is to design and implement the reliable and energy efficient architecture for LTE uplink system using FPGA. IFDMA is the most energy efficient subcarrier mapping scheme of SC-FDMA multiple access scheme. In IFDMA, the data symbols subcarrier mapping is not one to one instead each subcarrier carries a part from each data symbol transmitted at that time instant. The reason for the selection of IFDMA subcarrier mapping along with SC-FDMA multiple access scheme for LTE uplink comes mainly from its advantage to provide a low peak to average power ratio (PAPR) for the transmitted waveform. This results in less power consumption in the mobile station during uplink transmission. The reliability of the system is improved using interleaving process by avoiding packet loss. Convolution codes are less complex and are used to provide error free transmission. The enhancement of energy efficiency is done using the convolution coded IFDMA. The chosen energy efficient architecture must be more power efficient and support high data rates, which is the main requirement for the mobile user. The proposed reliable and energy efficient architecture for LTE uplink system is implemented using Xilinx system generator tool.

In broadband wireless communication systems, single-carrier transmission with frequency domain equalization (SC-FDE) is regarded as an alternative modulation technique to the orthogonal frequency division multiplexing (OFDM). Compared with OFDM systems, SC-FDE has similar implementation complexity and performance. However, SC-FDE with linear equalizer will suffer from serious performance deterioration under deep frequency selective fading channels. An effective method to solve this problem is to introduce non-linear decision feedback equalization (DFE) to SC-FDE. In this paper, a low complexity iterative decision feedback equalizer in the frequency domain for single- carrier systems is proposed. Based on the minimum mean square error (MMSE) criterion, a simplified parameter estimation method is introduced to calculate the coefficients of the feed-forward and feedback filters, which reduces the implementation complexity of the equalizer. Simulations show that the performance of the proposed algorithm is similar to the traditional iterative block DFE (IBDFE) under various multipath fading channels but with lower complexity.

Summary form only given. Emerging demands for high data rate multimedia based services and high spectral efficiency are the key drives for the continued technology evolution in wireless communications. Recently, several advancements have been introduced for 3G wireless communication systems to further enhance the data rate and the system performance. However, due to the proliferation of wireless multimedia applications and services such as video teleconferencing, network gaming, and high-quality audio/video streaming, it is apparent that 3G wireless systems will be unable to comply with this ever increasing demand for broadband wireless services. The next generation wireless communication systems (namely, fourth generation (4G) or beyond 3G (B3G) systems) are expected to support much higher data rate services compared to evolving 3G systems (up to 100 Mbit/s in outdoor environments and up to 1 Gbit/s in indoor environments). The major technical challenges will be achieving high spectral efficiency and handling high frequency-selectivity due to the use of large bandwidth. Hence, it has become crucial to incorporate the recent technical advances in the physical layer into the future wireless systems. In this keynote speech, an overview of leading technological advances and future trends in the physical layer that enable truly ubiquitous broadband wireless capabilities will be presented. The topics include multiple-input multiple-output (MIMO) technologies, adaptive modulation, cooperative diversity, multicarrier CDMA, ultra wideband (UWB) transmission, and cognitive radio.

The present paper gives an overview of multiple access techniques proposed for the uplink in future wireless communication systems. This paper provides the comparison between Orthogonal Frequency Division Multiple Access (OFDMA) and Single-carrier frequency division multiple access (SC-FDMA) techniques. A survey of Uplink Multiple Access Techniques in LTE Mobile Communication System, their basic features and various issues related to this have been introduced in this paper.

In this paper, the reconfigurable annular ring slot antenna with circular polarization diversity is proposed for SDMB(satellite digital multimedia broadcasting) system. The proposed antenna consists of a ring slot with tuning stubs. Four PIN diodes are attached to achieve circular polarization diversity. By switching the diodes on or off, the proposed antenna can be operated either RHCP(right hand circular polarization) mode or LHCP(left hand circular polarization) mode. The experimental result shows that the proposed antenna has an impedance bandwidth( VSWR les 2 ) of 2.47~3.04 GHz(570 MHz) at LHCP mode, an impedance bandwidth( VSWR les 2 ) of 2.45~3.01GHz(560 MHz) at RHCP mode, a maximum gain of 3.1dBi at RHCP mode, 4.76dBi at LHCP mode. The 3dB CP bandwidth of about 100 MHz at both RHCP and LHCP mode is achieved at the center frequency 2.63 GHz. The proposed antenna is suitable for application such as mobile satellite communications, WLAN(wireless local area networks), and broadband wireless communication systems.

To meet the increasing need of high-data-rate and broadband wireless communication systems, the devices and its circuits R&D under Millimeter, Sub-Millimeter, or even Terahertz (THz) frequency bands are attracting more and more attention from not only academic, but also industrial areas. Most of the former research on the THz waveband (0.1–10 THz) antenna design is mainly focused on realizing high directional gain, such as horn antennas, even though the coverage area is very limited when comparing with the current Wi-Fi system. One solution for the horizontally omnidirectional communication antenna is using the structure of multiple split-ring resonators (MSRRs). Aiming at this point, a novel 300 GHz microstrip antenna array based on the dual-surfaced multiple split-ring resonators (DSMSRRs) is proposed in this paper. By employing the two parallel microstrip transmission lines, different MSRRs are fed and connected on two surfaces of the PCB with a centrally symmetric way about them. The feeding port of the whole antenna is in between the centers of the two microstrip lines. Thus, this kind of structure is a so-called DSMSRR. Based on the different size of the MSRRs, different or multiple working wavebands can be achieved on the whole antenna. Firstly, in this paper, the quasi-static model is used to analyze the factors affecting the resonance frequency of MSRRs. Simulation and measured results demonstrate that the resonant frequency of the proposed array antenna is 300 GHz, which meets the design requirements of the expected frequency point and exhibits good radiation characteristics. Then, a dual-band antenna is designed on the above methods, and it is proved by simulation that the working frequency bands of the proposed dual-band antenna with reflection coefficient below −10 dB are 274.1–295.6 GHz and 306.3–313.4 GHz.

This paper considers the problem of tracking a dynamic sparse channel in a broadband wireless communication system. A probabilistic signal model is firstly proposed to describe the special features of temporal correlations of dynamic sparse channels: path delays change slowly over time, while path gains evolve faster. Based on such temporal correlations, we then propose the differential orthogonal matching pursuit (D-OMP) algorithm to track a dynamic sparse channel in a sequential way by updating the small channel variation over time. Compared with other channel tracking algorithms, simulation results demonstrate that the proposed D-OMP algorithm can track dynamic sparse channels faster with improved accuracy.