.3 The Gpp Lte Downlink Ofdma System Resource Allocation Study

With high-speed wireless services increasingly in demand, conflict between limited radio resources and increasing QoS (Quality of Service) requirements for various mobile services has become more and more urgent. In order to reconcile this conflict, Orthogonal Frequency Division Multiplexing (OFDM) has been introduced as a very promising technique which can support high speed data transmission, combate against multipath interference as well as provide high spectral efficiency.On the other hand, 3GPP has initiated its study on LTE (Long Term Evolution) for B3G (Beyond 3G) radio access in order to maintain the future competitiveness against other wireless communication standards such as Wimax. LTE could be regarded more as a revolution rather than evolution since it employs some matured B3G technologies such as OFDMA (Orthogonal Frequency Division Multiple Access).This dissertation starts with an introduction on key technologies of the Physical Layer in LTE system ,including uplink and downlink transmission scheme,OFDM,frame structure,main parameters,physical layer procedure etc. OFDM divides the entire transmission bandwidth into several orthogonal subcarriers,then splits high-rate datastream into a number of lower rate streams that are transmitted simultaneously over a number of subcarriers.As an extension, OFDM could be used more than just a modulation scheme, but as part of the multiple accesss technique as well, namely OFDMA. In an OFDMA system, system resources (subcarrier,bit,power) are assigned to the users dynamically according to channel state information ,thus to improve utilization efficiency of the system. The problem of assigning subcarriers and power to the different users in an OFDMA system has recently been an area of active research. A single subcarrier is regarded as the basic allocation unit in most of the previous works done in the area of adaptive resource allocation algorithm, which results in high complexity and huge amount of feedback information. By introducing grouping OFDMA system, a certain number of consecutive subcarriers , defined as RB(Resource Block), is regarded as the basic allocation unit in this dissertation. This dissertation studies adaptive resource allocation algorithm in an OFDMA system and applies a two-step method in order to lower the complexity by first allocating resource blocks to appropriate users then adjusting power and number of bits transmitted on each resource block. This dissertation proposes an idea that by reallocating the"Residual Power"in the system, more data could be transmitted on some resource blocks therefore improve the overall system performance. Chapter 3 proposes two algorithms based on the idea of"Residual Power".The proposed algorithms can achieve higher system throughput while fulfilling users'Qos requirement such as bit error rate and transimission rate. Chapter 4 proposes an adaptive resource block allocation scheme which could be used in the LTE downlink OFDMA system. The proposed scheme solves the resource allocation problem subject to constraints on total power, bit error rate, and proportionality among user data rates. It first allocates system resources based on the number of data that could be transmitted on each resource block and then adjust the allocation according to"User Satisfaction Rate"in order to guarantee the approximate proportionality among user data rates.At last the scheme further improves overall system throughput by reallocating the"Residual Power". Simulation results show that the algorithms and scheme proposed in this dissertation outperform static resource allocation schemes. And reallocating"Residual Power"could furthermore improve system performance.