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Cognitive radio networks are receiving a lot of research attention lately. Most user equipment in state-of-the-art wireless communication systems are equipped with two antennas. In this paper, we take advantage of the two transmit antennas in an underlay cognitive radio network scenario. Secondary users use the two transmit antennas in order to insert a null in the direction of the primary base station,...
The latest generation of wireless networks use OFDMA (Orthogonal Frequency Division Multiple Access) transmission technology in the downlink (e.g, WiMAX and LTE). The downlink is divided into bandwidth units and UEs (User Equipments) are each allocated a subset of these. Since at most one UE is assigned to each of these units, downlink transmissions within a sector are orthogonal. However, the transmission...
This paper examines the impact of the uplink power control and base station (BS) antenna down tilt on the system level performance in a realistic multicell three dimensional channel model. The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) adopts single carrier frequency division multiple access (SC-FDMA) as an air interface. The intra-cell interference is thus avoided but the...
A new interference self-cancellation (ISC) method for Single Carrier-FDMA (SC-FDMA) systems is proposed to mitigate the inter-user interference caused by frequency offset or Doppler effect. By transmitting a compensation symbol at the first symbol location in each resource block, the energy leakage can be significantly suppressed. With little bandwidth and power sacrifice, the proposed method can...
The downlink capacity of cellular networks is known to be strongly limited by inter-cell interference. In order to mitigate this interference, a number of frequency reuse schemes have recently been proposed. In this paper, we compare the potential capacity gains of these schemes accounting for the random nature of traffic.
System-level simulations of packet-based orthogonal frequency-division multiple access (OFDMA) cellular networks require a proper consideration of the channel-dependent fast fading/scheduling in order to produce meaningful results. However, generating the time and frequency selective fast fading channels and performing detailed channel-adaptive scheduling for each user in a multi-cellular system is...
Fractional frequency reuse (FFR) has been actively studied in order to reduce inter-cell interference, especially for cell edge users in current orthogonal frequency division multiple access systems. However, the best resource block (RB) allocation to the edge users is limited by conventional FFR, which has subbands consisting of contiguous RBs. In this paper, we propose a band-distributed FFR scheme...
For a single user with multiple receive antennas, co-antenna interference can be the dominant source of impairment in a Spatial Multiplex Orthogonal Frequency Division Multiple Access (SM-OFDMA) system, particularly when correlation exists between spatial sub-channels. By exploiting knowledge of the channel response and combining it with Dynamic Sub- Carrier Allocation (DSA), the algorithm proposed...
This paper introduces a new method for distributed interference mitigation in full spectral-reuse OFDMA cellular networks. This considers the use of pre-defined frequency-domain power profiles helping make the interference more predictable across the subcarriers. We propose a method for computing the power profiles so as to maximize the capacity of the system in case of maximum throughput scheduling,...
This paper addresses the subcarrier and power allocation problem in the uplink of an OFDMA system under the cognitive radio environment. The objective is to maximize the sum-rate of secondary users, without causing adverse interference to the primary users. We formulate the optimization problem subject to the individual power constraints and the interference constraints. Since the problem cannot be...
We consider the problem of scheduling users with backlogged and finite buffers on the multiple OFDM carriers (channels) over the two hops of the relay-enabled wireless network. Motivated by the recent 802.16j standard, we consider two sub-carrier grouping models (PUSC, AMC). While the extent of diversity gain varies depending on the model, spatial reuse is common to both the models and is crucial...
In this paper, we solve for the optimal spectrum management of the sum-rate maximization problem in two-user symmetric interference channels. A sum-power constraint, or equivalently, equal power constraints are assumed. First, by solving a closed form equation, we explicitly obtain the optimal spectrum management in flat channels as an optimal combination of flat FDMA and flat frequency sharing, exploiting...
This paper investigates the effect of using different optimization criteria for dynamic subcarrier allocation in a single carrier - frequency division multiple access (SC-FDMA) system. Simulation results show that using the minimum bit error rate (BER) as the optimization criterion has the best BER performance and an almost optimal capacity performance. The other criteria referred to as maximum spectral...
In this paper, we propose distributed dynamic resource allocation schemes for future cellular networks to enable efficient utilization of the whole available frequency spectrum. Our algorithms are simple, so that fast resource allocation decisions can be made at the base stations. To enable coordination between base stations, our schemes require inter-base-station signaling of system state information...
In OFDMA cellular system, the inter-cell interference is the main interference of the system, which greatly degrades the system performance. In order to enhance cell average throughput and the cell-edge user's peak bit rate, a hybrid inter-cell interference mitigation scheme is proposed. The hybrid scheme combines the fractional frequency reuse scheme and the frequency hopping scheme, in which cell-edge...
In this paper, a joint power and subcarrier allocation scheme in single-cell uplink OFDMA systems is proposed based on game theory. Our goal is to maximize the power efficiency of each user under peak power constraint. For the purpose, a utility function is designed which can enhance the rate per joule of energy consumed greatly, and the existence and uniqueness of the Nash equilibrium of the function...
This paper investigates the system performances of the IEEE 802.16j system with mobile relays such as cell throughput and service coverage. It also focuses on resource management problems such as overlapped subchannel allocation (OVSA) and orthogonal subchannel allocation (ORSA) and relay power control such as simplified on-off mobile relay control (SOMRC). The performance of the proposed schemes...
This paper presents the optimum control interval for intra-cell fractional transmission power control (TPC) for a shared data channel employing frequency domain channel-dependent scheduling and adaptive modulation and coding (AMC) in the evolved UTRA uplink using single-carrier (SC)-FDMA radio access. The simulation results show that the best attenuation factor in the fractional TPC is approximately...
In this paper, we derived closed-form expressions for the SINR distributions in OFDMA cellular system using fixed relays. First of all, the intercell interference at the BS and the RS are characterized and it is found that the intercell interference power is successfully modeled as the average of it. From the interference power modeling, the pdfs of SINRs for the four uplink cases are analyzed. The...
The novel frequency rotation techniques for suppressing the path interference and increasing the frequency diversity gain are proposed in uplink IFDMA system. In IFDMA, the path interference in multipath fading channel and the reduction of frequency diversity gain degrades the error rate performance, especially more significantly as the number of simultaneous access users becomes large. For suppressing...
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