MAC Design in Pulse-Based Communication Systems

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

Ultra wideband-impulse radio (UWB-IR) systems transmit data by ultra short pulses. The UWB-IR systems can achieve a time diversity gain by transmitting some pulses for each information symbol. In L. Yang et al. (2002) the space time (ST)-UWB-IR system was proposed to achieve a space-time diversity gain by transmitting space-time block coded symbols with some antennas. In the ST-UWB-IR system, the transmit antennas transmit the same symbol over an ST code block simultaneously. If all the transmit antennas can transmit different symbols independently, that is, if it separates the symbols from each antenna, we can expect a higher transmission rate than the ST-UWB-IR system. Moreover, at the same transmission rate, we can expect a larger diversity gain by sending more pulses for each symbol. This paper proposes a space hopping (SH)-UWB-IR system. In the SH-UWB-IR system, to allow each user to transmit different symbols from different antennas, a unique time hopping sequence is assigned to each antenna, which is known to the receiver. In addition, to get the larger diversity gain in the SH-UWB-IR system, the transmitted symbols are interleaved over the transmit antennas. From the results of our computer simulation, we show that when the number of users is small, the bit error rate (BER) of the SH-UWB-IR system is superior to that of the ST-UWB-IR system at the same data rate.

In an ultra-wideband (UWB) impulse radio (IR) system, a number of pulses, each transmitted in an interval called a "frame," is employed to represent one information symbol. Conventionally, a single type of UWB pulse is used in all frames of all users. In this paper, IR systems with multiple types of UWB pulses are considered, where different types of pulses can be used in different frames by different users. Both stored-reference (SR) and transmitted-reference (TR) systems are considered. First, the spectral properties of a multipulse IR system with polarity randomization is investigated. It is shown that the average power spectral density is the average of the spectral contents of different pulse shapes. Then, approximate closed-form expressions for the bit-error probability of a multipulse SR-IR system are derived for Rake receivers in asynchronous multiuser environments. The effects of both interframe interference (IFI) and multiple-access interference (MAI) are analyzed. The theoretical and simulation results indicate that SR-IR systems that are more robust against IFI and MAI than a "conventional" SR-IR system can be designed with multiple types of ultra-wideband pulses. Finally, extensions to multipulse TR-IR systems are briefly described.

1.1 Impulse Radio (IR) Ultra Wideband (UWB) Communications Ultra wideband (UWB) communication is a fast emerging technology that offers new opportunities such as high data rates, low equipment cost, low power, precise positioning capability and extremely low interference Ghawami (2005). A wide range of possible UWB communication system applications includes radars due to UWB ultra high precision ranging at the centimeter level, wireless personal area networks (WPAN), sensor networks, imaging systems, UWB positioning systems, etc. Yang (2004), Kshetrimayum (2009). From a commercial point of view, the high data rates are the most attractive feature of UWB systems for which speeds of over 100Mb/s have been demonstrated Ghawami (2005). There exist three main types of UWB technologies: impulse radio (IR UWB), direct sequence (DS UWB), and multi-band orthogonal frequency division multiplexing (MB OFDM) Ran (2009). IR UWB communication technique is essentially different from all other communication techniques because it is carrier free and uses for communication between transmitters and receivers very narrow radio frequency (RF) pulses generated from the UWB pulse generator, while traditional transmission systems transmit information by varying the power, frequency, and/or phase of a sinusoidal wave in a modulation process Kshetrimayum (2009), Yao (2007). Consequently, complicated frequency mixers and local oscillators for carrier frequency up and down conversion are not necessary Yao (2007). IR UWB modulation techniques are especially important because the UWB spectrum has been made available by the Federal Communication Commission (FCC) and it can be used with IRs developed to date Lin (2005). Waveforms for IR UWB are designed to obtain a flat frequency response over the bandwidth of the pulse and to avoid a DC component. The large spectrum of a UWB signal may interfere with existing users. In order to keep this interference to the minimum, FCC specifies spectral masks for different applications, i.e. the allowed power output for specific frequencies Ghawami (2005). A contiguous bandwidth of 7.5GHz is available in the frequency interval of (3.1− 10.6)GHz at a maximum power output of −41.3dBm/MHz which is considered as extremely low Ghawami (2005). The power spectral density (PSD) of UWB systems defined as a ratio of the transmitted power P in watts and a signal bandwidth B in hertz is extremely low as compared to other communication systems due to the very wide bandwidth B of short pulses that are typically of nanosecond or picosecond order Ghawami (2005). The selection of the impulse signal type for IR UWB communication system is essential since it determines

This paper presents a System on a Chip (SoC) Field-Programmable Gate Array (FPGA) implementation for Media Access Control (MAC) layer of a fast industrial Wireless Local Area Network (iWLAN) protocol, which is used to control industrial robots in factory automation environments. This protocol is a potential technique for industrial wireless communication system by using the Low overhead Packet Division Multiple Access (PDMA) scheme controlled by MAC layer. In our previous research, the MAC layer hardware was implemented and tested on simulation software, but the SoC design for the MAC layer has not been implemented and real tested on the FPGA. In this paper, we have successfully implemented the SoC system for MAC layer of this high-speed wireless communication protocol on the FPGA.

The link budget of the transmission gain is usually evaluated by using the Friis' transmission formula. However, it is not directly applicable to ultra wideband impulse radio (UWB-IR) transmission systems. This paper presents the link budget evaluation formula in the term of transmission gain for the UWB-IR systems that takes into account the transmitted waveform, its distortion due to the antennas, the channel and the correlation receiver. Since the antennas are significant pulse-shaping filters in UWB-IR, the various kinds of the antennas are experimentally examined, especially focused on the effect of the received signal and the isotropic template waveforms.

Ultrawideband (UWB) signals are extremely power limited due to the severe power spectral density constraints obligated by the Federal Communications Committee. Therefore, the design of radiation efficient antennas for UWB signaling is a challenging step in the design and development of impulse radio UWB (IR-UWB) communication systems, especially when these signals coexist with previously standardized narrowband (NB) wireless services. In this paper, a dual-band-notched quad-element UWB multiple-input multiple-output (MIMO) antenna design is presented. The proposed design is capable of suppressing NB interference (NBI). The NBI suppression capability of the proposed design is tested both experimentally and through simulations. Moreover, the experimentally measured spectral characteristics of the proposed design are employed in simulating the bit error rate (BER) performance of IR-UWB systems, considering the biphase modulation (BPM) scheme. Both experimental and simulation results show that the proposed design is capable of improving the BER performance of BPM-modulated IR-UWB systems in an NBI environment by suppressing the NBI signals located at six different frequencies within the bandwidth of the two band notches of the proposed design, while introducing a negligible distortion to the IR-UWB signaling waveforms.

In-car wireless data communications systems require a short-range unlicensed radio communications technology that causes a very low level of interference in the other, already deployed radio links and networks, offers low and medium data rate, can reuse the already occupied radio-frequency (RF) bands, and assures low probability of message collisions. Ultrawide band (UWB) impulse radio employs RF pulses with very short duration to carry the information; consequently, it is an optimal candidate for the in-car wireless communications and intravehicular wireless sensor networks. Data rate and shape of RF carrier pulse determine the performance of a UWB radio link. To limit the interference caused, the maximum power radiated by an UWB device is restricted by the Federal Communications Commission (FCC) in the U.S. Introducing a new mathematical model and starting from the FCC regulations, analytical expressions for the calculation of FCC power limits are derived here. It is shown that the low- and high-rate UWB impulse radio systems are peak and average power limited, respectively. The relationship between the mathematical model and the parameters of an UWB carrier pulse used in a built UWB radio is established. The performances of RF carrier pulses known from the literature are evaluated and compared. All expressions derived are verified by measurements.

With the onset of multimedia applications, Quality of Service (QoS) in 802.11-based wireless ad hoc networks has been an essential area to look into. Standard wireless protocols such as IEEE 802.11b and IEEE 802.11e have been deemed unsuitable for multimedia traffic transmission in an ad hoc (multihop) network environment due to the unique network characteristics. As an ad hoc network is infrastructureless and distributed in nature, it gives rise to several challenges in QoS provisioning. In this thesis, we focus on the research of three key areas on QoS in ad hoc networks namely, buffer management in the medium access control (MAC) layer, cross-layer design and flow admission control. Firstly, we study MAC layer buffer management in the IEEE 802.11e protocol. The IEEE 802.11e MAC protocol provides QoS for multimedia traffic by probabilistic priority queueing. Ad hoc networks tend to generate a large volume of network control packets for route maintenance and these control packets are typically queued in the highest priority queue. As a result, higher priority control traffic is always being served, consuming most of the bandwidth and results in poor network performance for data traffic. We examine this problem and propose a dynamic buffer management scheme to mitigate it. By setting different threshold levels in different priority queues, we allow lower priority data traffic to be served when the higher priority control traffic is deemed to be excessive. Simulation of our proposed scheme has shown that our approach yielded better network performance compared to the standard protocol in terms of packet delivery ratio and average delay. Secondly, we study the cross-layer interaction between the MAC and Network layers to identify its impact on QoS. We select the IEEE 802.11e MAC protocol and Ad-hoc On Demand Distance Vector (AODV) routing protocol in our study since they are standardized protocols for wireless networks. In IEEE 802.11e MAC protocol, lower priority traffic has a higher probability of being blocked. Hence, the MAC layer will inform the Network layer of a broken link through the link notification function. In this case, AODV will re-route the paths that traverse this link. As a result, higher priority traffic which shares the same link as the lower priority traffic will undergo the same re-routing procedures. We termed this phenomenon path correlation effect. Under high traffic load, the path correlation effect will be more intense and hence degrade the QoS of higher priority traffic. To break the path correlation effect, we propose a cross-layer design called the Bundled Virtual Circuit (BVC). Our proposed BVC scheme not only addresses the path correlation issues, but also provides priority treatment from the Network layer to the MAC layer. Through our simulations, our proposed cross-layer design approach is proven to provide better network performance than the 802.11e/AODV protocols in terms of packet delivery ratio and delay. Finally, we examine flow admission control at the routing layer in ad hoc networks. Standard routing protocols such as AODV performs routing on a shortest path basis. In the presence of multiple routes, hotspots are likely to form among the intermediate nodes and thus lead to network congestion. In addition, existing routes are not well-protected from the introduction of new routes. We propose a flow admission control algorithm to be used with AODV. Our algorithm allows routes to be created through available bandwidth and congestion estimation. During the route discovery phase, each node will be gauged on its estimated available bandwidth and its backlog of packets in the MAC buffer. If a node does not have sufficient bandwidth, or has too many backlogged packets compared to the requested flow rate, it will not participate in the route discovery process. From simulations, our new scheme is able to provide better network performance than the standard AODV protocol in terms of delay. Our work in this thesis focuses on QoS provisioning in ad hoc networks from the MAC and network layer perspectives. By studying the network characteristics and protocols’ behavior, we investigate the various problems of providing QoS in an ad hoc network environment and propose three different schemes to improve the QoS provisioning at the MAC and network layers. We believe that our work is able to provide some insights to the research area on QoS in ad hoc networks.

We propose Low Density Parity Check (LDPC) coded optical wireless communication systems with multiple subcarrier modulation (BPSK and QPSK). Upper bounds on the bit-error rate (BER) for maximum likelihood (ML) decoding of LDPC coded systems have been obtained on atmospheric optical channels where the effects of the scintillation exist. We also show that LDPC coded atmospheric optical systems have better BER than Turbo coded atmospheric optical systems.

Over the past few years, mobile networks have emerged as a promising approach for future mobile IP applications. With limited frequency resources, designing an effective MAC (Medium Access Control) protocol is a hot challenge. IEEE 802.11b/g/a/n networks are currently the most popular wireless LAN products on the market [1]. The conventional IEEE 802.11b and 802.11g/a specification provide up to 11 and 54 Mbps data rates, respectively. However, the MAC protocol that they are based upon is the same and employs a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) protocol with binary exponential back-off. IEEE 802.11 DCF (Distributed Coordination Function) is the de facto MAC protocol for wireless LAN because of its simplicity and robustness [2,3]. Therefore, considerable research efforts have been put on the investigation of the DCF performance over wireless LAN [2]. With the successful deployment of IEEE 802.11a/b/g wireless LAN and the increasing demand for real-time applications over wireless, the IEEE 802.11n Working Group standardized a new MAC and PHY (Physical) layer specification to increase the bit rate to be up to 600 Mbps [3]. The throughput performance at the MAC layer can be improved by aggregating several frames before transmission [3]. Frame aggregation not only reduces the transmission time for preamble and frame headers, but also reduces the waiting time during CSMA/CA random backoff period for successive frame transmissions. The frame aggregation can be performed within different sub-layers. In 802.11n, frame aggregation can be performed either by A-MPDU (MAC Protocol Data Unit Aggregation) or A-MSDU (MAC Service Data Unit Aggregation). Although frame aggregation can increase the throughput at the MAC layer under ideal channel conditions, a larger aggregated frame will cause each station to wait longer before its next chance for channel access. Under errorprone channels, corrupting a large aggregated frame may waste a long period of channel time and lead to a lower MAC efficiency [4]. On the other hand, wireless LAN mobile stations that are defined as the stations that access the LAN while in motion are considered in this chapter. The previous paper analyzed the IEEE 802.11b/g/n MAC performance for wireless LAN with fixed stations, not for wireless LAN with mobile stations [5, 6, 7, 8, 9, 10]. On the contrary, Xi Yong [11] and Ha Cheol Lee [12] analyzed the MAC performance for IEEE 802.11 wireless LAN with mobile stations, but considered only IEEE 802.11 and 802.11g/a wireless LAN specification. So, this chapter summarizes all the reference papers and analyzes the IEEE 802.11b/g/a/n MAC performance for wireless LAN with fixed and mobile stations. In other words, we will present the analytical evaluation of saturation

Beam-steering-based optical wireless technologies are being widely investigated due to the capability of providing high-speed wireless connectivity in indoor applications. However, high-speed indoor optical wireless systems are traditionally realized with discrete bulky components, significantly limiting their practical applications. In this Letter, we demonstrate an infrared optical wireless communication system employing a miniaturized silicon integrated photonic circuit for beam steering for the first time. Experimental results show that up to 12.5Gb/s optical wireless communication can be achieved with error-free performance over a free-space range of 140cm, and limited mobility of users can be realized. The experimental results of this Letter open the way for realizing integrated high-speed optical wireless communications.

The compressed sensing(CS) theory has provided a new solution for the low-rate sampling design of Impulse Radio Ultra-WideBand (IR-UWB) signal. This paper gives full consideration of the influence of quantization noise in IR-UWB system, and designs an effective quantization and reconstruction mechanism with high performance of resisting noise. Based on the analysis of noise distribution characteristics in compressed sampling value, the signal reconstruction model is revised, and then the performances of Dantzig-Selector (DS) method, Subspace Pursuit(SP) method, and traditional reconstruction algorithms are compared. On this basis, a signal reconstruction method (hybrid DS-SP method) with self-adaptability in DS and SP is proposed. Based on hybrid DS-SP method and consideration of overload uniform quantization, overload hybrid DS-SP mechanism is proposed which considered both the digital rear-end and analog front-end of IR-UWB receiver under compressed sensing framework. Simulation results show that the overload hybrid DS-SP mechanism achieves the exceptional reconstruction performance compared to the traditional reconstruction algorithms under different noise conditions with a compromised complexity between DS and SP.

A design of wireless communication system, particularly Media Access Control (MAC) and Physical layer system (PHY) for Factory Automation (FA) system based on Wireless Local Area Network (WLAN) communication system, is proposed in this paper. The designed of MAC is synchronous multi-user round-robin transmission protocol. Low overhead Packet Division Multiple Access (PDMA) scheme is utilized for Multi-user Downlink transmission up to 80 MHz, while Frequency Division Multiple Access (FDMA) is employed for the uplink transmission. The designed of PHY system is developed based on a fast and deterministic communication featuring the synchronous multi-user system. For efficient of multi-user transmission in the proposed protocol, the transmission time of the proposed iWLAN with 40 MHz bandwidth can achieve 500% better than PROFINET wireless standard. Furthermore, the implementation results of MAC and PHY layer of the proposed system show that FPGA logic utilization can fit with the target FPGA which is promising for a full implementation and evaluation combining with radio frequency.

In this paper, we consider blind interference suppression in IR UWB communication system, and the means of a statistical technique called independent component analysis (ICA), taken as a solution for the coexistence of impulse-radio Ultra-wideband (IR-UWB) systems with other wireless systems was studied. Particularly for the evaluation of the system performance, tone, multiton, and partial-band interference signals are considered at very low signal to interference ratio. The performances showed that ICA is a very good method for interference suppression in IR-UWB system.