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In general, link-adaptive schemes, such as adaptive modulation and coding (AMC) and hybrid automatic repeat request (HARQ), enhance system capacity in time-varying wireless channels. For these link-adaptive schemes to be applied, resources have to be adaptively and dynamically allocated every frame. Thus, the system needs control messages to send information to users about dynamic resource allocation. Such information includes user ID, resource position, level of modulation, and coding and automatic repeat request (ARQ) information. However, the transmission of these resource-allocation messages causes control overhead. In this paper, we introduce a scheme that applies AMC to the transmission of resource-allocation messages and analyze its performance in systems that support truncated ARQ, such as link-layer ARQ and HARQ. In addition, we show that using AMC to transmit control messages is a good way to reduce control overhead; in particular, it is very effective when the number of users per frame is large, as in voice over Internet Protocol (VoIP) services. Index Terms--Adaptive modulation and coding (AMC), control messages, control overhead, resource allocation.

We propose a new location tracking scheme for subscribers on transportation systems (TSs) in which a large number of fast-moving users have the same location as the TS. The group location tracking (GLT) scheme in which a group location update is performed instead of the IS-41's individual location update has been proposed. We propose a distributed GLT (DGLT) scheme based on several virtual visitor location registers (VVLRs) and representative identities. We analyze the GLT and DGLT schemes in view of the database (DB) access cost as well as the signaling cost under one-dimensional network architecture. Compared with the IS-41 scheme, the schemes based on group management generally have a lower signaling cost and a lower DB access cost due to a significant reduction in the number of location updates. user mobility increases or the number of users on a TS increases the performance of the group management schemes improves. The DGLT scheme, in which a corresponding home location register selects a closest VVLR among several possible VVLRs, generally has a lower signaling cost although a DB access cost is increased slightly compared with the GLT scheme. We also obtain the regions in which the DGLT is more efficient than the IS-41 and the GLT scheme. The DGLT scheme is an appropriate solution for high signaling cost systems and the GLT scheme is useful for high DB access cost systems. Index Terms--Location management, location update, mobility.