Orthogonal Frequency Division Multiple Access in WiMAX and LTE: A Comparison S Srikanth and P A Murugesa Pandian, Anna University Xavier Fernando, Ryerson University Group – D10VT6 INTRODUCTION USE OF OFDMA IN WIMAX AND LTE NETWORK ENTRY STEPS IN WIMAX AND LTE PERFORMANCE BOUNDS FOR SYNCHRONIZATION AND CHANNEL ESTIMATION EVOLUTION OF WIMAX AND LTE Nhóm CONCLUSION INTRODUCTION - IEEE 802.16e-based WiMAX and Third Generation Partnership Project (3GPP)-based Long Term Evolution (LTE) are the two standards that are likely to dominate the fourth generation (4G) wireless landscape - Both LTE and WiMAX standards use several common technologies with subtle differences.The main common technology is orthogonal frequency-division multiple access (OFDMA) - There are many good reasons for choosing OFDMA such as multipath handling capability, scalability of operation in different bandwidths, the ability to handle different data rates, and the ability to easily combine with multiple antenna techniques Nhóm - The focus of this article is on the comparative use of OFDMA in LTE and WiMAX systems USE OF OFDMA IN WIMAX AND LTE Nhóm FRAME STRUCTURE USE OF OFDMA IN WIMAX AND LTE RESOURCE MAPPING FROM SUBCARRIERS Subcarriers are the smallest granular units in the frequency domain, OFDM symbol duration is the smallest granular unit in the time domain in OFDMA systems In WiMAX, subchannels are formed from a group of In LTE, 12 adjacent subcarriers are grouped as a unit in the subcarriers in an OFDM symbol frequency axis, and OFDM symbols (or OFDM symbols in A slot is formed by combining a subchannel with different special cases) are considered as a unit in the time axis numbers of OFDM symbols In LTE, the uplink uses SCFDMA, which can be viewed asdiscrete Fourier transform (DFT)-spread OFDMA The data is passed through a DFT block before being input to the Nhóm OFDMA module USE OF OFDMA IN WIMAX AND LTE USE OF FREQUENCY DIVERSITY subcarriers for OFDM symbols parts of the spectrum - Another RB can be used in the second slot of the subframes - This pseudorandom selection of the positions of the subcarriers - Control messages use small bunches of contiguously placed - Control messages are also sent using this diversity-based subcarriers spread out over the entire bandwidth subchannelization method - In LTE, an RB (Resource Block) contains the same 12 contiguous are formed by grouping 24 subcarriers that are present in different Nhóm - In WiMAX, use PUSC (Partially Used Sub-Carrier), subchannels - Within an OFDM symbol, no FD USE OF OFDMA IN WIMAX AND LTE USE OF MULTIUSER DIVERSITY - In WiMAX, the BAMC organize groups of contiguous subcarriers - Each bin has data &1 pilot subcarriers, and such contiguous bins are grouped in a band user feeds back the best bands - Based on this, BS chooses bins in one of these bands and allocates the same bin over three consecutive OFDM symbols - Frequency diversity and MUD-based transmission cannot coexist in time - In LTE, BTS uses the channel feedback from the mobile to schedule an RB for the user in a frame - The feedback can be periodic - Different modes of channel feedback - Channel feedback can be sent as one value for the entire operating the entire bandwidth - In LTE both can be used Nhóm bandwidth or as a sequence of values for a sequence of subbands covering USE OF OFDMA IN WIMAX AND LTE USE OF INTERFERENCE DIVERSITY - The subcarriers used in a reference subchannel in a reference cell are - In LTE, there can be a clash in the positions of the data subcarriers that distributed in different subchannels in the reuse cells The subcarriers can be used in neighboring cells used in a subchannel in a certain cell are unlikely to be repeated in a - There is no interference diversity particular subchannel in another cell provided the downlink perm base values are Nhóm different NETWORK ENTRY STEPS IN WIMAX AND LTE SYNCHRONISATION - In WiMAX, a preamble is transmitted at the start of every frame - In LTE, the frame synchronization is obtained by detecting the primary - The preamble signal is generated by using every third subcarrier in the synchronization sequence (PSS) allowed bandwidth - Unlike the preamble in WiMAX, the number of subcarriers used for PSS - The pseudorandom sequence to be sent on the subcarriers is specified in is fixed the IEEE 802.16e standard - The Zadoff-Chu sequence loaded onto the subcarriers is specified in the - A mobile uses the time domain properties of the preamble sequence, standard along with the structure of the cyclic prefix (CP) - ID of the PSS in the received signal gives two potential starting points in - Since the duration of the CP is not fixed, a search procedure might have the frame as there are two PSS transmissions in the frame Nhóm to be performed to obtain the CP duration NETWORK ENTRY STEPS IN WIMAX AND LTE NETWORK ENTRY In WiMAX, a mobile has to search for a valid preamble to acquire frame synchronization Once synchronized, the mobile reads the frame control header (FCH) message, which points to the length of the DL-MAP message that contains the various allocations in the frame In LTE, irrespective of bandwidth and the number of subcarriers, the first step remains the same for all mobiles: locating the primary synchronization signal (PSS) and secondary synchronization signal Nhóm (SSS) PERFORMANCE BOUNDS FOR SYNCHRONIZATION AND CHANNEL ESTIMATION WiMAX PUSC mode: Maximum delay spread Nhóm Maximum Doppler spread Maximum Doppler spread LTE Considering both the pilots carrying symbols: ~22us PERFORMANCE BOUNDS FOR SYNCHRONIZATION AND CHANNEL ESTIMATION PHYSICAL LAYER OVERHEAD In WiMAX The overhead due to the use ofpreambles and pilots in every OFDM symbol isgiven by the ratio : In LTE In LTE Nhóm The subcarriers used for physical layer processing purposes are the ones that carry reference The subcarriers used for physical layer processing purposes are the ones that carry reference symbols, plus primary and secondary synchronization sequences symbols, plus primary and secondary synchronization sequences EVOLUTION OF WIMAX AND LTE The WiMAX and LTE camps have submitted candidate proposals to satisfy the official requirements of the ITU IMTAdvanced criterion for 4G wireless systems WiMAX to WiMAXv2 LTE to LTE-A channel bandwidths Forming distributed and contiguous localized the OFDMA related features are very similar in both resourceunits (DRUs and LRUs) The aggregation of multiple carriers to obtain wider Forming fixed size physical resource units (PRUs) Nhóm Base on the IEEE 802.16m standard WiMAXv2 and LTE-A CONCLUSION Nhóm This article has compared the use of OFDMA in WiMAX and LTE standards in detail Thanks For Listening ... choosing OFDMA such as multipath handling capability, scalability of operation in different bandwidths, the ability to handle different data rates, and the ability to easily combine with multiple. .. antenna techniques Nhóm - The focus of this article is on the comparative use of OFDMA in LTE and WiMAX systems USE OF OFDMA IN WIMAX AND LTE Nhóm FRAME STRUCTURE USE OF OFDMA IN WIMAX AND LTE. ..INTRODUCTION USE OF OFDMA IN WIMAX AND LTE NETWORK ENTRY STEPS IN WIMAX AND LTE PERFORMANCE BOUNDS FOR SYNCHRONIZATION AND CHANNEL ESTIMATION EVOLUTION OF WIMAX AND LTE Nhóm CONCLUSION INTRODUCTION