No abstract

No abstract

No abstract

No abstract

No abstract

In LTE system, it is difficult for an eNB to properly allocate uplink resource blocks (RBs) to UEs as many factors complicate the issue. So far, most research has focused on maximizing system throughput. However, this is often achieved by downgrading other performance metrics and may result in the waste of resources. In this paper, a resource allocation scheme for LTE uplink is proposed which takes into account the data rate granted by call admission control (CAC). Data rate is defined based on exponentially weighted moving average (EWMA). The scheme leads to a close match between user demand and resources actually allocated, thereby making better use of the resources. In addition, robust modulation-coding is considered in resource allocation. Results obtained via simulation show that the proposed scheme demonstrates good performance in important aspects compared to other resource allocation methods.

No abstract

The 802.11 has emerged as the prominent wireless LAN technology as the mobile computing devices such as notebooks and PDA have replaced the desktop computers to be the main trend products. However, if the number of active stations is large, that is high-loading condition for the legacy DCF of 802.11, the capacity will be very low due to high collision costs. In this paper, we introduce the TDMA concept to partition all numerous active stations into several groups to avoid all stations transmitting the frames simultaneously. When Point Coordinator (PC, generally referring to AP) finds that the number of active stations (M) is large i.e. bigger than 8, it broadcasts number of groups (N g ) and group head (N h ) bits (such as 00000100 00000000) information in the TIM field of the beacon frame. Once all stations receive this instruction, the stations which last two LSB bits of the MAC address (IEEE EUI-48 or EUI-64) are 00 belonging to group 0 will transfer their frame first. On the contrary, all stations belonging to other groups will set their waiting time, that is, Network Allocation Vector (NAV) much more precisely. Analysis shows that the capacity of our GB-DCF will be near to the theoretical capacity limit of 802.11 WLAN even if the distributions of all active stations among all groups are not so uniform. This capacity could be independent of the number of active stations and CW Max (Contention window maximum). In this article, we also introduce the grouping cycle concept to our scheme, called GB-DCF + , to reduce the heavy overhead of the legacy DCF and to increase the MAC layer throughput of the upcoming 802.11n protocol. The key idea of GB-DCF + is that DIFS, SIFS, and ACK are added to the grouping cycle which consists of the transmissions of all groups' slot instead of a single frame. Simulations show that the capacity of our scheme could approach to 45.1% when the PHY data rate, frame size, number of stations, and number of groups are 216 Mbps, 2160 bytes, 128, and 32 respectively. On the contrary, the capacity of DCF will be low to 19.3% with the same scenario. This is due to the tremendous collision costs as well as fixed and heavy overhead of the legacy DCF.