Georgios Orfanos

An error model for inter-vehicle communications in highway scenarios at 5.9GHz

The design and evaluation of Inter-Vehicle Communication (IVC) protocols rely much on the accurate and efficient computational simulations. For simulations of Medium Access Control (MAC) and higher layers, the modeling work of underlying Physical layer (PHY) and wireless channel has impacts both on the computational efficiency of simulations and on the correctness of results. In this contribution, we discuss the modeling issues of the inter-vehicle wireless channel in highway scenarios and the packet error performance of Dedicated Short Range Communications (DSRC) PHY, which works at the newly allocated 5.9GHz Intelligent Transportation System (ITS) frequency band. A computationally efficient yet accurate enough error modeling approach used in our MAC layer simulator WARP2 is presented in this paper, together with simulation results. Both weaknesses and potential improvements of the proposed approach are discussed also in this work.

MC-CDMA based IEEE 802.11 wireless LAN

In this paper, a modified version of the IEEE 802.11a protocol is proposed and evaluated. We combine multicarrier code division multiple access (MC-CDMA), a novel, high capacity multicarrier modulation technique, with the standard medium access control (MAC) protocol of the 802.11 wireless local area network (WLAN). The suggested system utilizes spread spectrum to divide the channel bandwidth into parallel codechannels, and allows for a number of mobile terminals to share the medium in a more fair and efficient way. The proposed system has been evaluated using a protocol simulator, MACNET-2, and the performance results are discussed in this paper.

MIMO Link Modeling for System Level Simulations

MIMO (multiple input - multiple output) systems apply multiple antennas to increase signal to noise ratio (SNR), reduce interference and/or send multiple streams simultaneously over a single channel. Besides increasing the data rate of the physical layer (PHY), benefits can be achieved with cross-layer optimization approach exploiting the layered structure of the channel. In this paper we focus on MIMO schemes with multiplexing and/or diversity gain and present a link model for system level simulations. The model maps total SNR to achievable link level throughput, both per spatial subchannel and cumulative. The model can be combined with an arbitrary coding and modulation scheme and is abstract enough to be applied to any system protocol, fulfilling the given conditions about channel propagation characteristics

Error probabilities for radio transmissions of MC-CDMA based W-LANs

IEEE 802.11a/e has become a worldwide wireless local area network (W-LAN) standard, with a rapid development. Many proposals have been made for its further expansion, and some of them focus on multicarrier code division multiple access (MC-CDMA), a novel, high capacity, multicarrier modulation scheme. In this paper we present an analysis of the error models for radio transmissions in such systems. An accurate model of the channel is necessary for the performance evaluation of the protocol by means of computer simulations. Focusing on the estimation of the signal to interference and noise ratio (SINR) at the detector and on the calculation of a packet error ratio (PER), in this contribution we discuss a modeling approach which allows an efficient calculation of frame transmissions over a MC-CDMA shared radio channel.

An adaptive MAC protocol for MC-CDMA ad hoc wireless LAN

Multi-carrier code division multiple access (MC-CDMA), a novel, high capacity, multicarrier modulation scheme, is developing to a key radio transmission technology for future wireless local area networks (W-LANs). However in ad hoc code division multiple access (CDMA) networks near-far effects can block a receiver due to high interference. These effects occur when a receiving station is closer to an interferer than to its corresponding transmitter. Accordingly, the receiver cannot detect the intended signal out of the received one and the data transmission fails. In this work, we present an adaptive medium access control (MAC) protocol for ad hoc MC-CDMA based W-LANs, based on the IEEE 802.11 MAC protocol. The new protocol has the ability to overcome the near-far-problem by employing a frequency adaptation method. The key of the proposed method is an interference estimate built at each receiving mobile station (MS). Aided by its estimate, a MS can calculate whether the quality of service (QoS) expectations of the incoming link can be accomplished. If the interference is too high, the receiving MS initiates a frequency channel change and informs the corresponding transmitter over the control packets about the Id of the new channel. It is shown that this concept can deploy the high capacity characteristics of MC-CDMA in wireless environments

A Centralized MAC Protocol with QoS Support for Wireless LANs

Wireless local area networks (WLANs) are widely used in homes and offices, as well as in public places, mainly as the last mile of an Internet connection, but also as an interconnection between different devices. This extensive usage of WLANs, with the need of modern applications (such as voice over IP) for high throughput and low transmission delays, impose the necessity for efficient protocols with quality of service (QoS) support. In previous work the ability of multi carrier-code division multiple access (MC-CDMA) based medium access control (MAC) protocols to achieve high efficiency has been demonstrated. This paper presents a MAC protocol, based on MC-CDMA that uses an access point (AP) to centrally control the network and provide QoS support. Extensive simulation results and a comparison with the standard IEEE 802.11e prove the efficiency of the proposed protocol.

A primary adaptation of the W-CHAMB protocol for Gigabit WPANs

High speed WPANs are intended to provide multi-media and multi-megabyte transmission services over relatively short distances for a wide range of devices. The long term goal of future high speed WPANs is to support transmission with a data rate of up to 2 Gbps. The W-CHAMB protocol is a link layer protocol for next generation WLANs. It is able to perform multi-hop delivery of high quality multi-media services in a fully distributed manner. In this article, we adapt the W-CHAMB protocol for Gigabit WPANs. The analytical results on the traffic performance and system capacity indicate that the adapted protocol is able to support high amounts of high quality multi-media transmission services in multi-hop Gigabit WPANs

Interference aware adaptive MAC protocol for MC-CDMA ad hoc wireless LANs

Multi-carrier code division multiple access (MC-CDMA) is recently considered as a key technology for future wireless systems. Its high capacity and collision avoidance capability can fulfill the increasing demand for high throughput and quality of service (QoS). The application of MC-CDMA divides the frequency channel in many parallel channels, separated from each other in code domain. We refer to these parallel channels as code channels (cchs). In order to exploit the advantages of this spread spectrum technique, the medium access control (MAC) protocol has to be aware of the multichannel structure of the MC-CDMA network. Mobile stations (MSs) should be equally distributed among the cchs for better utilization of the resources and collision avoidance. Additionally, the assignment of a link to a cch should be done under consideration of the interference situation in the network. This is very important for the prompt operation of the link as the different cchs loose their orthogonality in asynchronous systems. In this paper we present an adaptive, interference aware MAC protocol for MC-CDMA adhoc wireless local area networks (WLANs), which adapts the allocation of resources to both interference and utilization degree of the different cchs, in order to achieve high capacity

A modified IEEE 802.11 MAC protocol for MC-CDMA

In this paper, we introduce a modified version of the IEEE 802.11a protocol and evaluate its performance. The new protocol is a combination of the standard Medium Access Control (MAC) protocol of 802.11 and the Multi-Carrier Code Division Multiple Access (MC-CDMA) scheme, a novel, high capacity multicarrier modulation technique. The system can achieve higher throughput and shorter delays, owing to the division of the spectrum in a number of parallel codechannels.