Reverse spreading device, timing detecting device, channel estimating device, frequency error measurement method and automatic frequency control method
View Patent ↗A reverse spreading device is provided which is capable of performing timing detection and channel estimation even in a large frequency offset environment without great increases in its circuit scale and its power consumption and of expanding a range being within the AFC (Automatic Frequency Control) for the frequency offset. A multiplication is made by multipliers between complex base band signals and spread codes and then resulting n-pieces of multiplied values are integrated by m-pieces of adders for every k-pieces of multiplied values to produce m-pieces of complex intermediate signals before obtaining complex symbols. A probability of correct synchronization is increased by providing a frequency offset to m-pieces of complex intermediate signals using phase rotators to compensate for rotation within one symbol period and to obtain a great spreading gain. A range being within the AFC for the frequency offset is expanded since a phase error is corrected before a production of the complex symbol signals.
1. A method for measuring a frequency error being a difference between a reference frequency of a receiver and a reference frequency of a sender comprising the steps of:
counting how many chips of complex base band signals are to be input;
performing a rotation correction in a step-by-step manner by rotating a phase of said complex base band signal on a complex plane at a phase rotation angle at m-stages each being slid by a reference rotation angle being an angle obtained by dividing a rotation angle (2π) of a revolution to M portions every time said counted number of the chips increases by K-chips;
producing a multiplied value by multiplying the rotation corrected complex base band signals by spread signals;
producing a correlation value of I component of said multiplied value and a correlation value of Q component of said multiplied value by adding said multiplied value in an accumulative manner for every I component and every Q component during one symbol period;
calculating a power value of the complex base band signal in said one symbol period based on said correlation values of said I component and said Q component; and
selecting said reference rotation angle so that said power value becomes maximum.
2. The method according to claim 1 , further comprising detecting said frequency error based on said reference rotation angle selected.
3. A reverse spreading device for reversely spreading complex base band signals, each of said complex base band signals being composed of an I component and a Q component and being spread by spread codes, said device comprising:
a frequency error corrector to count how many chips of said complex base band signals to be input and to perform a rotation correction in a step-by-step manner by rotating a phase of said complex base band signals on a complex plane at a phase rotation angle at m-stages each being slid by a reference rotation angle every time a count of the chips increases by K-chips;
a spread code multiplier producing a multiplied value by multiplying each of the rotation corrected complex base band signals by said spread codes;
two accumulative adders to produce a correlation value of I component of said multiplied value and a correlation value of Q component of said multiplied value by performing accumulative addition of said multiplied value for one symbol period;
a power calculator calculating a power value of said complex base band signal in said one symbol period based on said correlation values of said I component and said Q component; and
a selector selecting said reference rotation angle so that said power value becomes maximum.
4. The device according to claim 3 , further comprising a frequency error detector detecting a frequency error based on said reference rotation angle selected by said selector.
5. A timing detecting device, comprising: the reverse spreading device of claim 3 ; and a peak detecting circuit configured to receive the correlation value of the I component and the correlation value of the Q component, and detect spreading timing as a function of sizes of the correlation values of the I and Q components.