IEEE 802.15.4 is a standard defined for wireless sensor network applications with limited power and relaxed throughput needs. The devices transmit data during two periods: Contention Access Period (CAP) by accessing the channel using CSMA/CA and Contention Free Period (CFP), which consists of Guaranteed Time Slots (GTS) allocated to individual devices by the network coordinator. The GTS is used by devices for cyclic data transmission and the coordinator can allocate GTS to a maximum of only seven devices. In this work, we have proposed two algorithms for an efficient GTS allocation. The first algorithm is focused on improving the bandwidth utilization of devices, while the second algorithm uses traffic arrival information of devices to allow sharing of GTS slots between more than seven devices. The proposed schemes were tested through simulations and the results show that the new GTS allocation schemes perform better than the original IEEE 802.15.4 standard.

Wireless communication is being developed in the last years day by day, there are several standards that talks about it. We are going to go through the IEEE standard 802.11 which talks about wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. Looking this more carefully we will study MAC specifications and its environment. The work that ISY department at Institute of Technology of Linkoping University has proposed is to design a MAC sublayer implementation for WLANs using C language programming and testing it with the test environment called “test bench”. This test bench will simulate LLC sublayer and PHY layer, in this way, our MAC implementation will has to interact with it. Therefore we will simulate a wireless network where we are going to have a short number of stations and we are going to look at carefully the MAC sublayer response in an ad hoc network.

This thesis will investigate the possibilities to wireless communicate within time critical applications with the radio protocol IEEE 802.15.4. IEEE 802.15.4 is a very quick protocol so the delays and jitter can be ignored in a small network. The thesis handles the question: Is it possible to split a CAN-bus and send the data via radio to the other side of the CAN-bus? The big problems with this are: • Will it be treated like a transparent link and not disturb the original functionality? • How does a system which is split up by radio treat new nodes on the bus? • What will be the maximum speed and the maximum utilization factor for the split up bus? • What new suitable protocols can be implemented on a higher level to get the split bus to work? This is modeled and discussed, real measurement from a radio link is used in the model to see if it’s possible. The radio communication will satisfy the demands from the company regarding their application. With an efficient error handling and a smart transmission protocol the application can be a very smart way of sending CAN-data via radio. / Denna rapport undersöker möjligheterna med att kommunicera trådlöst i tidskritiska applikationer med hjälp av radioprotokollet IEEE 802.15.4. IEEE 802.15.4 är ett väldigt snabbt protokoll så jitter och fördröjningen i sändningarna kan försummas för så små nätverk som tas upp i denna uppsats. Går det att bryta en CAN-buss och koppla in denna radiolänk så att den uppfattas som transparent? Många problem kommer att dyka upp om detta görs, några av dem är dessa: • Hur behandlar ett system nya noder som kopplas in om CAN-bussen är uppdelad? • Vilken är den maximala hastigheten och utnyttjandefaktor som kan uppnås av den delade CAN-bussen? • Måste ett överliggande protokoll användas för att sköta om datatrafiken mellan bussarna? Detta modelleras och diskuteras efter det att de uppmätta mätvärdena har samlats in och analyserats. Det som framkom var att det fungerar väldigt bra, data kommer fram i tid och felen i radiosändningarna är väldigt små. Med en väl genomtänkt felhantering och ett likaså genomtänkt omsändningsprotokoll kommer detta att fungera väldigt bra beroende på avstånd och antennval.

Vehicular ad hoc networks (VANETs) are an extreme case of mobile ad hoc networks (MANETs). High speed and frequent network topology changes are the main characteristics of vehicular networks. These characteristics lead to special issues and challenges in the network design, especially at the medium access control (MAC) layer. Due to high speed of nodes and their frequent disconnections, it is difficult to design a MAC scheme in VANETs that satisfies the quality-of-service requirements in all networking scenarios. In this thesis, we provide a comprehensive evaluation of the mobility impact on the IEEE 802.11p MAC performance. The study evaluates basic performance metrics such as packet delivery ratio, throughput, and delay, as well as the impact of mobility factors. The study also presents a relation between the mobility factors and the respective medium access behavior. Moreover, a new unfairness problem according to node relative speed is identified for both broadcast and unicast scenarios. To achieve better performance, we propose two dynamic contention window mechanisms to alleviate network performance degradation due to high mobility. Extensive simulation results show the significant impact of mobility on the IEEE 802.11p MAC performance, an identification of a new unfairness problem in the vehicle-to-vehicle (V2V) communications, and the effectiveness of the proposed MAC schemes.

For ultra-wideband (UWB) communications, acquisition is challenging. The reason is from the ultra short pulse shape and ultra dense multipath interference. Ultra short pulse indicates the acquisition region is very narrow. Sampling is another challenge for UWB design due to the need for ultra high speed analog-to digital converter.<p>A sub-optimum and under-sampling scheme using pilot codes as transmitted reference is proposed here for acquisition. The sampling rate for the receiver is at the symbol rate. A new architecture, the reference aided matched filter is studied in this project. The reference aided matched filter method avoids using complex rake receiver to estimate channel parameters and high sampling rate for interpolation. A limited number of matched filters are used as a filter bank to search for the strongest path. Timing offset for acquisition is then estimated and passed to an advanced verification algorithm. For optimum performance of acquisition, the adaptive post detection integration is proposed to solve the problem from dense inter-symbol interference during the acquisition. A low-complex early-late gate tracking loop is one element of the adaptive post detection integration. This tracking scheme assists in improving acquisition accuracy. The proposed scheme is evaluated using Matlab Simulink simulations in term of mean acquisition time, system performance and false alarm. Simulation results show proposed algorithm is very effective in ultra dense multipath channels. This research proves reference aided acquisition with tracking loop is promising in UWB application.

Web browsing via Wi-Fi wireless access networks has become a basic function on a variety of consumer mobile electronic devices, such as smart phones, PDAs, and the Apple iPad. It has been found that in terms of energy consumption, wireless communications/networking plays an important role in mobile devices. Since the power-saving mode (PSM) of the IEEE 802.11 a/b/g standard is not tailored for the HTTP protocol, we propose a novel power saving scheme that exploits the characteristics of web applications. After sending HTTP requests, the proposed power saving scheme updates the estimated value of RTT based on the information contained in the TCP timestamp header field. Next, the proposed scheme adjusts the value of the listening period based on the estimated value of RTT. When all TCP connections have been closed, the wireless network card could enter the deep-sleeping mode. In this case, the value of the listening period could be larger than one second, since the user is reading the webpage and is unlikely to send another HTTP request within one second. The usage of the deep-sleeping mode can significantly reduce the power consumption of mobile devices.

The thesis is mainly in algorithm design and implementation of hardware circuit of baseband signal processing at the transceiver of 2450 MHz band chirp spread spectrum in IEEE 802.15.4a ¡V 2007 Low Rate-Wireless Personal Area Network (LR-WPAN). Due to the characteristic of LR-WPAN such as low cost, low power consumption, small size and easy to implementation, we have to take the complexity and the system performance into consideration. In this thesis, we study on the algorithm design of baseband signal, and analysis the simulation result. At the transmitter, following the specification and realize it. At the receiver, designing the algorithm including the packet detection, energy detection and down-sampling, carrier frequency offset estimation and compensation, timing synchronization, and bi-orthogonal demapper. The system performance after quantizing is 3dB better than the receiver sensitivity we expected. After finishing the algorithm design of the transceiver, we implement the baseband signal circuit by using Verilog Code. Finally, we make an application to National Chip Implementation Center (CIC), and will measure the circuit after the chip tape out. The circuit is fabricated in a 0.18-£gm CMOS technology.

Multimedia applications in wireless communication have shown notable increases over recent years. Specifically, Quality of Service (QoS) has become an important support mechanism in the context of a variety of applications which utilize network resources. The IEEE 802.16 standard for Wireless Metropolitan Area Networks (WirelessMAN) provides a complete QoS control structure designed to enable flow isolation and service differentiation over the common wireless interface. Although the media access control (MAC) mechanisms defined in this standard can offer predefined QoS provisioning on a pre-connection basis (additionally, many algorithms have been addressed to support QoS guarantees for various kinds of applications), the design for a stable, efficient and flexible MAC scheduling algorithm for such QoS provisioning still remains to be discovered. In this paper, we propose a QoS control scheme, Efficient Bandwidth Allocation (EBA), for the WirelessMAN system. Notably, this schedule enables predefined service parameters to control the service provided for each uplink connection and it provides each connection with different service opportunities such that the BS could allocate the most suitable bandwidth constantly for each connection with the various QoS parameters. Moreover, through MAC layer resource allocation, the proposed algorithm is capable of providing QoS guarantee for the SSs under different distance.

The IEEE 802.11a has become the mainstream protocol used in modern wireless communication system due to its high propagation rate of data (54 Mb/s). To meet high propagation rates, the communication devices used in IEEE 802.11a protocol usually present a high conversion gain and a high linearity (denoted as third order intercept point, IIP3). The IIP3 of conventional up- and down-conversion mixers are only about 0 dBm and -5 dBm, which fail to achieve a high propagation rate of data. This thesis utilizes the TSMC 0.18 £gm CMOS technology to design and fabrication up- and down-conversion mixers with very high linearity for IEEE 802.11a application. The proposed high-linearity up-conversion mixer with 1.01 mm ¡Ñ 0.85 mm chip size and its wide bandwidth (5~6 GHz) is well suited for IEEE 802.11a application. To enhance the linearity and bandwidth, a transconductor stage with gm-boosted structure, a switch stgae with LO-body grounded structure and a load stage with shunt peaking structure are adopted in this research. Under 5.2/5.4/5.8 GHz operating frequencies, the implemented up-conversion mixer demonstrates a high conversion gain of 6.8/7.1/6.3 dB and a high linearity of 8.9/9/13.2 dBm, respectivly. In addition, a moderate consuming power (6.86 mW) of such mixer can be achieved at 1.2 V supply voltage. On the other hand, this thesis also designed and fabricated a high-linearity down-conversion mixer with chip size of 1.02 mm ¡Ñ 0.86 mm and 5.2 GHz center frequency. To improve the linearity and isolation and reduce the high-order noise, a transconductor stage with dual-gate structure and a load stage with RC-tank structure are adopted in this research. According to the EM-simulation resutls, the proposed down-conversion mixer presents a moderate conversion gain of 6 dB and a high linearity of 0.8 dBm. Additionly, a moderate consuming power (6.75 mW) of such mixer can be achieved at 1.8 V supply voltage.

The Distributed Coordination Function (DCF) which uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) and binary slotted exponential backoff scheme is the basis of the IEEE 802.11 Medium Access Control (MAC) protocol. However, the DCF is not suitable for real-time traffic control since the backoff scheme may cause huge frame delay and jitter. We propose a modified DCF which uses a forward backoff scheme to remedy this disadvantage. In addition, a call admission control (CAC) is also proposed. Our protocol can guarantee service qualities such as the network throughput, frame delay, and jitter for real-time traffics. Besides, the modified DCF is still compliant with the IEEE 802.11 standard. Simulation results have shown that our method performs better than other DCF disciplines.