Research On Ranging Technique In Ofdm Systems

Up-link synchronization In OFDM system is completed by ranging. The result of ranging affects the terminal access rate, dropping rate and base station coverage directly. A good ranging algorithm needs to strike a balance between performance and efficiency. Although there are many ranging algorithm in the industry, but every algorithm has advantage and disadvantage, and different scope. For systems base on IEEE 802.16e, some of existing algorithms need large amount of computation, or have not optimal performance, or are protected by some company's patents. So finding a simple and practical algorithm In accordance with the characteristics of our base station has practical significance.In this thesis, we design a ranging scheme base on IEEE 802.16e. Using sufficient ranging sub-channels while retaining the most sub-channels in theory for data transfer.A ranging code detecting method is proved, the characteristics of which are as follows: The ranging signal received in ranging sub-channels is conjugate correlated in frequency domain with the local ranging codes. The result is calculated in downlink IFFT module. The result contains the power information. Two decision thresholds are set, one is power sum, another is the rate of power peak to power sum. They are used to determine whether there are ranging codes. The position of power peak is time offset. The advantage is less computing. And reusing the downlink IFFT module can save hardware resource. Two thresholds can improve the detection rate, and reduce the false alarm rate of ranging codes.A method is present, which uses two symbols power information to expand the detection range of initial ranging code. It solves the problem that one detection value corresponding to a number of situations and makes the base station support the terminal far away from 6.857 km to 24 km. Receiver with two antennas, combined with the power antenna combined method, can improve receive gain.By simulation, it shows that the new algorithm is better than TI's reference algorithm at 0 dB, of which the detection rate improved by 11 percentage points. Then detail how to achieve the ranging detection in FPGA, which include the function modules division and circuit implementation. In many of them, simplified hardware techniques are used to reduce the cost of resources. Final test of the circuit shows that the advantages of this circuit are less resources cost, high detection rate and low false alarm rate and missed rate.