Chapter 2 - High data rates in mobile communication

The nature of future wireless applications demands high data rates. Naturally dealing with ever-unpredictable wireless channel at high data rate communications is not an easy task. The idea of multi-carrier transmission has surfaced recently to be used for combating the hostility of wireless channel and providing high data rate communications. OFDM is a special form of multi-carrier transmission where all the subcarriers are orthogonal to each other. OFDM promises a high user data rate transmission capability at a reasonable complexity and precision. At high data rates, the channel distortion to the data is very significant, and it is somewhat impossible to recover the transmitted data with a simple receiver. A very complex receiver structure is needed which makes use of computationally expensive equalization and channel estimation algorithms to correctly estimate the channel, so that the estimations can be used with the received data to recover the originally transmitted data. OFDM can drastically simplify the equalization problem by turning the frequency-selective channel into a flat channel. A simple one-tap equalizer is needed to estimate the channel and recover the data. Future telecommunication systems must be spectrally efficient to support a number of high data rate users. OFDM uses the available spectrum very efficiently which is very useful for multimedia communications. For all of the above reasons, OFDM has already been accepted by many of the future generation systems [1].

Power efficient ultra-wideband based wireless communication for wireless body area network applications

In the modern world, bandwidth and data rates are two most important parameters under consideration in any communication system. An optical fiber communication system is capable of transmitting the data at high bit rates and has a large bandwidth capacity. This high data rate and bandwidth capacity in an optical fiber communication system is further enhanced by using wavelength division multiplexing (WDM) in conjunction with the information transmission system, in which information from multiple sources are transferred using the same fiber, at the same time, but at different wavelengths. But the high capacity and data rates in optical WDM system is limited by nonlinear effects that occur in optical WDM system, which not only pose a limitation on the channel capacity and data rates but also degrades the performance of the data transmission system. In this paper, analysis has been done to investigate the efficiency of Four Wave Mixing (FWM) effect under the influence of different system parameters such as chromatic dispersion coefficient, channel spacing, transmission power level, effective area of fiber and fiber length in the form of input signals and output signals frequency spectrums.

In this paper, a pulse positioned-differential phase shift keying technique is proposed for providing high data rate in satellite optical communications. Polarization-rotation based DPSK is employed to avoid the use of delay-line interferometers, which is a major impairment for multi-rate DPSK. Furthermore, a novel modulation format suitable for polarization-rotation based DPSK is proposed for higher data rates. The performance enhancement of the proposed technique is theoretically demonstrated compared to conventional differential phase shift keying. The simulation results show that a high data rate could be obtained with the proposed technique. Therefore, high data rate and multi-rate differential phase shift keying can be realized using the proposed technique for next-generation satellite optical communication.

A large number of phone calls and data services will take place in indoor environments. In Long Term Evolution (LTE), femtocell, as a home base station for indoor coverage extension and wideband data service, has recently gained significant interests from operators and consumers. Since femtocell is frequently turned on and off by a personal owner, not by a network operator, one of the key issues is that femtocell should be identified autonomously without system information to support handover from macrocell to femtocell. In this paper, we propose a dynamic reservation scheme of Physical Cell Identities (PCI) for 3GPP LTE femtocell systems. There are several reserving types, and each type reserves a different number of PCIs for femtocell. The transition among the types depends on the deployed number of femtocells, or the number of PCI confusion events. Accordingly, flexible use of PCIs can decrease PCI confusion. This reduces searching time for femtocell, and it is helpful for the quick handover from macrocell to femtocell. Simulation results show that our proposed scheme re- duces average delay for identifying detected cells, and increases network capacity within equal delay constraints. The 3rd Generation Partnership Project (3GPP) is work- ing on the standardization of asynchronous communication systems. This technology is being enhanced gradually en- suring higher user data rate, bigger system capacity, and lower cost. The wideband CDMA (WCDMA) system is standardized with 3GPP release 99/4 which is being de- ployed in the world. Release 5 is related to High Speed Downlink Packet Access (HSDPA), and it improves the downlink packet transmission speed theoretically up to 14.4 Mbps. High Speed Uplink Packet Access (HSUPA) is enhanced up to 5.76 Mbps in uplink, and it is standardized with the Release 6. We simply mention both HSDPA and HSUPA as High Speed Packet Access (HSPA). In release 7, High Speed Packet Access Evolution (eHSPA, HSPA+) is standardized. eHSPA is based on the HSPA network with a simple upgrade, and it supports more bandwidth efficiency and lower latency. The maximum data rate is 28.8 Mbps in downlink and 11.5 Mbps in uplink (1). How- ever, users still require further system improvements. The technology is dramatically enhanced in release 8, where the standard of Long Term Evolution (LTE) is currently being established. The main objectives of LTE are higher data rates, lower latency, increased capacity, enhanced coverage, and an optimized system for the packet switching network (2). LTE also considers a femtocell, which is referred to as a home base station for an indoor coverage extension and overall network performance enhancement (3). Recently, LTE-Advanced standard targeting of 1Gbps for low mobil- ity is being discussed in release 9. We look into general features and requirements of fem- tocells. Important issues related to access control are de- scribed, followed by our contributions and organization of the paper.

Electronic system U3iflfl ULSI wi11 be based on ultrasmall features for ULSI monolithic circuits and on small f eatures for advanced packaging such as multi-chip modules (MCMs). These reduced interconnection cross sections are needed to achieve very high density circuits but may conflict with achieving very high data rates across thos e interconnections. Optical interconnections may provide both very high density interconnections and very high speed data rates. Most comparisons of optical with electrical inter. onnection emphasize the high speed bipolar circuits rather than the high density CMOS circuits. However within VLSI/ULSI systems CMOS interconnections are quite different from and offer several advantages (particularly lower power dissipation at the system level) over bipolar LSI interconnections. The role of optical interconnects is viewed here from the perspective of the CMOS interconnection environment. L

Radio frequency identification (RFID) is an exciting, rapidly growing, multi-disciplinary field with emerging technologies and applications. Today RFID is a generic term for technologies that use radio frequencies to automatically identify people or objects. In a typical RFID system, digital information is transferred between a base station and movable objects, using wireless communication techniques. The base station, called reader, is usually a complex device connected to a host computer or network. The movable objects are simple, inexpensive devices called tags, which are attached to people or objects to identify. In far-field RFID, coupling mechanism between reader and tag is based on propagation of electromagnetic waves. Passive, far-field tags don't contain a power source, but rely on wireless power transmission instead; they are powered by rectification of radio signal sent by reader. These tags send data to reader by changing load connected to their antenna in a coded manner, a technique known as backscatter modulation. As of today (2009), passive RFID tags that are commercially available are typically optimized for operating at a large distance from reader. This inevitably comes at cost of a low data transfer rate. A new field in RFID is currently emerging, which focuses more on data rate than on operating range. The development of such high data rate RFID tags, communicating at several megabit per second (Mbps), opens way to a variety of promising applications in areas of ambient intelligence and the internet of things. A typical example is wireless memory tag, which consists in a passive, far-field RFID tag containing high capacity, high speed nonvolatile memory. Such tags enable to store multimedia content (video, music...) that can be downloaded by user in a few seconds. In near future, this will probably become a popular new distribution method for various digital products. Designing such tags involves a number of challenges. Because they communicate at high data rate, they consume a significant amount of power. Particular care must be taken in order to optimize efficiency of wireless power transmission, so that tags can reach a decent operating range. This thesis work discusses how various tag building blocks, such as antenna and rectifier, impact efficiency. The principle of wireless voltage regulation is introduced. It allows to further improve efficiency by lowering losses not only in tag, but also in reader. Various experimental results are provided, which show amongst other things that power emitted by reader can be reduced at least by a factor of four. Realizing passive, far-field tags that can transfer information at high data rate with backscatter modulation is not a trivial task. This work aims to determine how to maximize useful backscattered power, which conveys information. Because reader has a finite sensitivity, it needs to receive a minimum backscattered power to recover data, which limits tag operating range. This research project brings to light a fundamental limitation concerning reader sensitivity, and proposes a model to estimate maximum tag reading range. In order to be widely accepted by market, an important characteristic of these tags is that they must be very inexpensive. Hence, tag's integrated circuit (IC) can't be realized using high performance, but costly, fabrication processes. For this reason, this research project focuses on tag ICs realized in a mainstream CMOS process, which implies specific challenges. In particular, impact on architecture and power efficiency of rectifier is discussed. There are basically two approaches to design high data rate, passive, far-field RFID tags. The first one is to base design on a single frequency architecture, and to use a unique carrier frequency for both wireless power transmission and communication. The other approach is use a dedicated carrier frequency for each of these two links, which leads to dual frequency architecture. This thesis work presents a practical design example for each of these architectures, including various experimental results. Both tag ICs are realized using UMC CMOS 0.18 µm technology. When reader emits 3.3 W effective isotropically radiated power (EIRP) at 866.6 MHz, and 10 mW EIRP at 2.44 GHz, dual frequency tag can be read at 10 Mbps at an operating range of 33 cm. The tag's rectifier reaches a power efficiency of 36%. As of today, this tag outperforms commercial products and published works in area of high data rate, passive transponders.

An efficient base station (BS) power allocation scheme for the forward link is proposed to to improve the overall throughput in a multicell high data rate (HDR) system, which is designed to support a high data rate. In HDR, if a cell is properly designed, users located close to a BS acquire an excessive signal to interference power ratio (SIR) for a maximum achievable data rate. This excessive power results in lower SIR for users at cell boundary. By allocating lower power for users near a BS than the maximum power, other-cell interference can be alleviated to users near the cell boundary. Even though HDR adopts time division duplexing (TDD) type of scheduling, the capacity can be increased through the control of interference. Simulation results validate the throughput gain, which is about 6/spl sim/9% under ideal condition.

The emerging trends of wireless communication and ever growing demand of very high data rate from users created the need for new technologies that could satisfy this need under limited bandwidth. A 60-GHz Ultra-Wideband (UWB) system that can support up to 7 Gbps data rate, which is 10 times faster than the data rate of the Wi-Fi 802.11n, is one of the promising options. The system utilizes higher order modulation and advanced coding schemes known as Adaptive Modulation and Coding (AMC). However, inappropriate selection of modulation level and coding rate can lead to low data rate particularly in the presence of Radio Frequency interference and multipath fading. Moreover, further performance degradation occurs when non-optimal decoder due to code constraint length was selected. This paper proposes and evaluates a duplex 60-GHz UWB system employing Orthogonal Frequency Division Multiplexing (OFDM-UWB) to boost the data rate and extend the coverage. Firstly, an OFDM-UWB system employing high order modulation that transmits data simultaneously over multiple carriers spaced apart at precise frequencies been simulated and validated using Matlab. Secondly, the system performance been analyzed when convolutional coding been introduced in term of Bit Error Rate (BER). The simulation results show that the BER performance of 16QAM is worse, with 6 dB penalties at BER of 10−3, compared with that of QPSK. Moreover, simulation also shows that there are 2 dB difference between the performance of R=1/2 and R=7/8, while the highest throughput been achieved when the 3/4 code rate is employed.

The Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) standard is becoming the appropriate choice to pave the way for the next generation wireless and cellular standards. While the popular OFDM technique has been adopted and implemented in previous standards and also in the LTE downlink, it suffers from high peak-to-average-power ratio (PAPR). High PAPR requires more sophisticated power amplifiers (PAs) in the handsets and would result in lower efficiency PAs. In order to combat such effects, the LTE uplink choice of transmission is the novel Single Carrier Frequency Division Multiple Access (SC-FDMA) scheme which has lower PAPR due to its inherent signal structure. While reducing the PAPR, the SC-FDMA requires a more complicated detector structure in the base station for multi-antenna and multi-user scenarios. Since the multi-antenna and multi-user scenarios are critical parts of the LTE standard to deliver high performance and data rate, it is important to design novel architectures to ensure high reliability and data rate in the receiver. In this paper, we propose a flexible architecture of a high data rate LTE uplink receiver with multiple receive antennas and implemented a single FPGA prototype of this architecture. The architecture is verified on the WARPLab (a software defined radio platform based on Rice Wireless Open-access Research Platform) and tested in the real over-the-air indoor channel.

The increasing interest on multimedia applications and services in portable computing communication will create at same time a large demand for high speed wireless data on communication devices. The 4th generation (4G) mobile communication is expected to offer 100 Mbps or higher data rates in downlink. orthogonal frequency division multiplexing (OFDM) and multiple carrier code division multiple access (MC-CDMA) are potential candidates for next generation of mobile radio communications for achieving hight data rate transmissions. In cellular networks, the frequency reuse is one of the main parameters to consider since it is more suitable to optimize the spectrum reuse. Using a frequency reuse factor of one, it could be a possible system using the same frequency in all the network. In this proposal the sensitivity and the impact of an interfering base station based on a MC-CDMA system is investigated and analyzed using different channel coding and decoding processes.

While use of power-efficient signaling schemes appears to be effective at compensating for the inherent high path-loss associated with pure diffuse infrared links, it begins to lose its effectiveness as the data rate is increased. At very high data rates, intersymbol interference (ISI) can result in a very high and sometimes irreducible power penalty, preventing the system from operating at a low bit-error probability. We use a link design employing a multibeam transmitter in conjunction with a narrow field-of-view (FOV) direction diversity receiver. The design goal is to eliminate the effect of ISI so that power-efficient signaling schemes such as pulse-position modulation (PPM) can be employed at very high data rates. We also use high-rate Reed-Solomon codes to further increase the power efficiency of PPM signals. The proposed system can be made rate-adaptive through varying modulation level L and/or code rate R without increasing the complexity significantly. This provides a dynamic range large enough to allow efficient utilization of available bandwidth, i.e., to allow portable terminals to communicate at their highest permitted data rate, without sacrificing the quality of service. It is shown that a bit error rate not exceeding 10/sup -9/ can be achieved within the link coverage area with 99% probability at bit rates up to a few hundreds of megabits per second, using transmitted power levels well below 1 W.

A unique underwater, high data rate, acoustic communications transceiver has been developed that has widespread commercial applicability. The unique properties of direct sequence spread spectrum are applied to mitigate both deep fading and intersymbol interference due to multipath. The transceiver is designed to provide full-duplex operation at a data rate of 625 bps per channel with high reliability. Considerably higher data rates are achievable with half-duplex operation. There is substantial operating margin in the very stressing scenario of 1 km range in the horizontal plane at 12 m depth (assuming a severe surface bounce). Additionally, spread spectrum processing gain provides added rejection of interference that falls in or near the transmission band. These capabilities represent a significant advancement in hydro-acoustic communications.

High data rate at high mobile speed will still be an essential requirement for the future 5G mobile cellular system. High frequency bands above 6 GHz are particularly promising for the 5G system because of large signal bandwidths such high frequencies can offer. By using high gain beamforming antennas, the problem of high propagation loss at high frequencies can be overcome. However, the use of beamforming antennas at such high frequencies requires a significant change in the design of a cellular system. In particular, it requires a significant change in key functions such as cell search, random access, measurement of beams for fast beam adaptation, and various physical control and data channels. In this paper, we propose a new radio frame structure for the future mobile cellular communications system at millimeter wave frequency that addresses such challenges. A testbed was built at Samsung Electronics, Korea, based on the proposed frame structure at 28 GHz with bandwidth of 800 MHz. It attained the downlink (DL) data rate of 7.5 Gbps by delivering four streams of 64 QAM data with code rate of 3/4 to two mobile stations (MSs) located in a close distance to the base station antennas at fixed positions. It also achieved the DL data rate of 1.2 Gbps by delivering single stream of 16 QAM data with code rate of 3/4 to an MS moving at 110 km/h in a single cell of up to 800 m in a line-of-sight environment. Finally, it implemented handover and achieved an average handover interruption time of 21 ms in a three-cell environment, and demonstrated feasibility of mobile cellular communications at millimeter wave frequency.

Ultra wideband (UWB) radio is a promising technology for short range wireless communications. It can be used for both high rate and low rate transmissions. High data rate can be achieved by using multiband (MB)-UWB approach whereas low data rate with robust system performance can be obtained by employing time hopping (TH)-UWB radio systems Majhi et al. (2006); Win & Scholtz (1998a). Nowadays, applications of UWB are spreading to various fields such as vehicle communications, wireless sensor networks, ad hoc wireless networks, and controller area networks. The most of the systems require low to moderate (1 kbs-100 mbs) data rates with an acceptable implementation cost. However, due to the presence of fast Fourier transform (FFT) and inverse FFT (IFFT), MB-UWB may not be a cost effective procedure for low data rate systems. Therefore, one needs an efficient system which adaptively changes the data rate from low to moderate with robust system performance. TH-UWB with OOK-PSM modulation provides low data rate with robust system performance Majhi, Madhukumar, Premkumar & Richardson (2008). However, it is possible to scale the TH-UWB radio system for low to moderate data rates by incorporating higher level modulation schemes with an adaptive method. For TH-UWB systems, various M-ary modulation schemes such as pulse positionmodulation (PPM), pulse amplitude modulation (PAM), pulse shape modulation (PSM), and their combined forms have been proposed to improve data rates and system performance with low complexities Bin et al. (2003); Durisi & Benedetto (2003); Ghavami et al. (2002); Michell et al. (2003); Usuda et al. (2004). However, due to the increase of inter symbol interference (ISI) in the presence of multipath channel, M-ary PPM or M-ary orthogonal PPM (OPPM) are not effective for TH-UWB systems with RAKE reception when M is high Foerster (2003); Win & Scholtz (1998b). High-level M-ary PAM is rarely used in short range and low power consumption communications systems Guvenc & Arslan (2003). This is because that the Euclidian distances between constellations become small with increase in M. Due to its robustness against ISI and multiple access interference (MAI), pulse-based modulation such as PSM has become an interesting research topic in TH-UWB, direct sequence UWB (DS-UWB) and transmitted referenceUWB (TR-UWB) radio systemsChu M de Abrue et al. (2003); Gezici et al. (2006); Hwang et al. (2007); Kim & Womack (2007); Parr et al. (2003). However, high-level M-ary PSM cannot be used due to the limited auto correlation properties 2