TAILIEUCHUNG - WiMAX Technology for Broadband Wireless Access 2007 phần 8

giữa các BSS nhưng mỗi BS có thể sử dụng các hoán vị khác nhau. Do đồng bộ hóa thời gian trong kịch bản này và biểu tượng thời gian dài của các biểu tượng OFDMA, chuyển giao nhanh chóng cũng như chuyển giao mềm là có thể. Cấu hình này có thể được sử dụng như một BS triển khai độc lập | Efficient Use of Radio Resources 189 among the BSs but each BS may use different permutations. Due to the time synchronisation in this scenario and the long symbol duration of the OFDMA symbol fast handovers as well as soft handovers are possible. This configuration can be used as an independent BS deployment with a controlled interference level. Coordinated synchronous configuration. All the BSs work in the synchronous mode and use the same permutations. An upper layer is responsible for the handling of subchannel allocations within the sectors of the base station making sure that better handling of the bandwidth is achieved and enabling the system to handle and balance loads between the sectors and within the system. The standard indicates that for TDD and FDD realisations it is recommended but not required that all BSs should be time-synchronised to a common timing signal. Radio Resource Management Procedures Power Control The support of power control procedure is mandatory in the uplink. The procedure includes both an initial calibration process and a periodic update process. By measuring the received power at the BS side the BS can send power offset indications to the MS which adjusts its transmit power level accordingly. It has to be noted that in the case where the MS uses only a portion of the subchannels the power density remains unchanged regardless of the number of subchannels actually used unless the maximum power level is reached . The power offset indication sent by the BS is consistent with the actual MCS that is to be used for the uplink transmission. Power adjustments related to the use of a different modulation scheme is then taken into account. Finally the power offset is also consistent with the maximum power that the MS can transmit indicated in the SBC-REQ MAC message . After reception of the power offset information the MS adjusts its transmit power according to Equation by simply adding the offset to the last value used for

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