Philippe Martins

A Layer 2 Scheme of Inter-RAT Handover between UMTS and WiMAX

The future B3G or 4G mobile networks will consist of heterogeneous networks, including GSM, UMTS, WiMAX and WIFI. In order to realize a seamless vertical handover (inter-RAT handover), a variety of interworking architectures and inter-RAT handover mobility managements have been proposed. Based on the integrated coupling architecture, we propose a novel common interworking sublayer (IW sublayer) at layer 2 on RNC and UE to provide a seamless PS inter-RAT handover between UMTS and WiMAX systems. This IW sublayer scheme focuses on eliminating packet loss and reducing handover latency which are common problems for most inter-RAT handover scenarios. Compared with other context transfer schemes, the simulation results show the IW sublayer with ARQ mechanism can achieve a lossless and prompt handover procedure. In addition, this IW sublayer scheme can eliminate false fast retransmit of TCP traffics which is usually caused by packet losses or out-of-order packet arrivals.

A layer 2 scheme for inter-RAT handover between UMTS and WiMAX in tight coupling architecture

The future B3G or 4G mobile networks will consist of heterogeneous networks, including GSM, UMTS, and WiMAX. In order to realize a seamless vertical handover (inter-RAT handover), a variety of interworking architectures and inter-RAT handover mobility managements have been proposed. In this paper we consider the tight coupling architecture to achieve the interconnection between UMTS and WiMAX systems. A novel common interworking sublayer (IW sublayer) is proposed at layer 2 on RNC, W-RNC and UE to provide a seamless PS inter-RAT handover between UMTS and WiMAX. This IW sublayer scheme, which features SR ARQ mechanism, focuses on eliminating packet loss and reducing handover latency that are common problems for most inter-RAT handover scenarios. The simulation results of the tight coupling architecture show that, compared with other context transfer schemes like buffering-and-forwarding of FMIPv6, the IW sublayer solution can achieve a lossless and prompt handover.

Subchannelization Performance for the Downlink of a Multi-cell OFDMA System

In this paper, different subchannelization modes for the downlink of a multi-cell OFDMA system are investigated. The frequency reuse factor is one. The subchannelization mode FUSC adopted in 802.16 is considered: frequency collision problem and partial loading are addressed. For a full loading factor, performances are compared with dynamic subcarrier allocation algorithms.

SCTP Extension for EGPRS/WLAN Handover Data

Multistreaming and multihoming SCTP features give better performance than TCP for the transport of signaling in wired networks. More recently, some solutions have been defined for wireless environment (Xing et al., 2002), mobile SCTP (mSCTP) is a wireless extension that was proposed to take benefit from the multihoming feature for hand off. In this paper we use SCTPs multihoming feature and define a new type of control chunk in order to retrieve radio information from mobile and to use this information to improve the performance of SCTP in handoff situation. We propose modifications of the SCTP congestion control algorithms to take into account information sent by mobile to the network (GGSN) via QoS_Measurement_Chunk. This new mechanism is useful to perform inter RAT handover for data. The example studied here is between EGPRS and WLAN. The results obtained are compared with the standard SCTP and present an improvement of performance especially in terms of throughput

Performance evaluation of L2 handover mechanisms, for Inter-Radio Access Networks

B3G networks will provide seamless data handover between different radio access technologies (RAT). In a near future, the WLAN access will be integrated in GPRS and UMTS radio access networks (RAN). During their communications, the subscribers will be able to switch automatically between the two technologies. In that case, their previous data transfer need to be re-established in the new RAT. This process must be carried out while minimizing the breakdown time and the data loss. This paper intends to evaluate the performances of handover policies between GPRS/UMTS and WLAN RAT and to propose adapted data handover strategies at layer two

Radio Aware SCTP Extension for Handover Data in EGPRS

SCTP is a transport protocol that is used in wired networks to transport PSTN signaling. It provides interesting features (namely multihoming and multistreaming) to enhance the performances of information transport over cellular networks air interfaces (S. Kang and M. Fields, 2003). Some additional extensions have been defined to adapt SCTP in a wireless context (mSCTP) (W. Xing et al., 2002). However current approaches do not take into account radio information in cell reselection/handover process. This study proposes a new extension for the SCTP protocol which aims at improving the transport performance in wireless environments. We define for that purpose a new control chunk (named Qos_measurement_chunk). It allows the emission of radio information from the mobile to the SCTP peer in the network. These information can be used by the SCTP layer to adapt the transmission rate to the current radio transmission conditions (particularly useful in handover/reselection situation). The combined use of Qos_measurement_chunk and of the multihoming feature provide a data handover with a performance improvement. The obtained simulation results are compared with the standard SCTP and present better performance in terms of data throughput in the access network

Interactions between the TCP and RLC Protocols in UMTS

Congestion control mechanisms, used in TCP, suffer from some performance issues when using them over wireless links. In this paper we investigate a TCP connection over the UMTS radio interface when using the RLC protocol in acknowledged mode. We compare protocol mechanisms used in TCP and RLC. The influence of the TCP congestion control mechanisms on the RLC buffer occupancy is analyzed and interactions between these two protocols are investigated.

A Cross-Layer Scheme for Inter-RAT Handover from WiMAX to UMTS

In future mobile networks, different radio access technologies, such as GSM, UMTS, WiMAX, WIFI, will coexist. In order to realize a seamless vertical handover (inter-RAT handover) among these technologies, a variety of interworking architectures and inter-RAT handover mobility managements have been proposed. Based on an integrated coupling architecture, we propose a novel common interworking sublayer (IW sublayer) at layer 2 on RNC and UE to provide a seamless PS inter-RAT handover between UMTS and WiMAX systems. This IW sublayer scheme focuses on eliminating packet loss and reducing handover latency which are common problems for most inter-RAT handover scenarios. In addition, an enhanced TCP proxy, which interacts with the IW sublayer, is also introduced to RNC to resolve other two typical inter-RAT handover problems of TCP traffics: BDP mismatch and spurious RTO. Compared with other vertical handover solutions, our novel inter-RAT scheme has the merits of keeping existing TCP protocol stacks unchanged and is robust to different handover scenarios. The simulation results show our total solution not only achieves a lossless and prompt handover procedure, but also accommodates BDP mismatch and prevents spurious RTO of TCP sender.

Comparison of Different Subchannelization Modes for OFDMA

In this paper, the problem of subchannel composition and allocation for the downlink of an OFDMA system is investigated. The subchannelization mode FUSC adopted in 802.16 is described and compared with dynamic subcarrier allocation algorithms. Performances are evaluated regarding spectral efficiency and complexity. Both single cell and multi-cell scenarios are considered.

The operation mode selection in FMIPv6

The fast handover for mobile IPv6 (FMIPv6) (Koodli, 2005) aims at reducing the long handover latency in mobile IPv6 (Johnson, 2004) by fast movement detection and fast binding update. Furthermore, it also reduces packet loss by buffering before the real link layer handover takes place. Due to uncertain link layer trigger time, however, the buffering mechanism sometimes introduces unacceptable handover latency for real-time traffics such as voice over IP (VoIP). In addition, if itpsilas the mobile node that makes the handover decision, FMIPv6 also suffers from uncertainty of handover target, which is unfavorable to TCP traffics such as FTP. In order to eliminate these negative effects, we propose that FMIPv6 should operate in predictive mode under the control of network if possible for TCP traffics. As to the VoIP traffic, in terms of the handover latency and packet loss requirements, a proposed hybrid mode is chosen adaptively. Numerical simulation results for the VoIP traffic demonstrate obvious performance improvement in terms of call drop rate and a new performance metric called packet cost.