Telefonaktiebolaget Lm Ericsson (publ)

Lars G Larsson

Perols B Gudmundson

Alex Krister Raith

Karim Jamal

Paul Mihkel Teder

Jon K Ugland

Hangkan Anders Persson

A mobile station can be connected to more than one base station in a procedure known as macro-diversity. In order to synchronize the signals for a specific cellular call connection, the time difference between the connected base station's signal and a macro-diversity candidate base station's signal is measured by a mobile station. This measurement is then transmitted to the network. The measurements can be used to achieve synchronization via frame staggering.

Time alignment of transmission in a down-link of CDMA system

In a digital time-shared transmission system, a receiver receives a signal whose symbol rate is lower than the channel bandwidth of the system. A correlating and sampling circuit receives a baseband signal, samples the signal a number of times with each symbol time, performs channel correlation, generates a channel estimate and samples down the once sampled signal to an observed signal with two values for each symbol time. A channel equalizer executes a fractional viterbi algorithm which utilizes two delta-metric values for each state transition and generates estimated symbols. A channel estimating filter receives a symbol sequence of alternating zero-value symbols and the estimated symbols and generates an estimated signal. The channel estimating filter is adapted with the aid of an error signal and the filter delivers a channel estimate to the channel equalizer. Weighting factors are generated with the aid of the error signal and the two aforementioned delta-metric values are co-weighted to a common delta-metric value with the aid of weighting factors, this common delta-metric value being used to generate the estimated symbols. The use of the weighting factors improves the metric calculation and enables the channel estimating filter and the channel equalizer to be relatively simple. The insertion of the zero-value symbols simplifies the generation of the weighting factors and the adaptation of the channel estimating filter.

Method and an arrangement of estimating transmitted symbols at a

Radio signals are transmitted over a fading radio channel and are filtered and sampled in a receiver to obtain a digital signal. A channel equalizer has an equalizing filter in which a channel estimate is formed with the aid of a known synchronizing sequence. A Viterbi analyzer decides symbols with the aid of the channel estimate. An estimated time derivative of the channel estimate is formed and adapted with the aid of the decided symbols. The channel estimate is adapted to the radio channel by the derivative estimate and the decided symbols. In the event of fading with rapidly varying signal strength, the channel estimate is adapted slowly and is predicted mainly through the derivative estimate which varies relatively evenly. The digital signal is stored in a memory and an initial value is formed for the derivative estimate as a difference between two known channel estimates divided by a time difference therebetween. The known channel estimate may belong to two separate synchronizing sequences or may belong to one synchronizing sequence and a fading time point in which the channel estimate has zero value.

Method of forming a channel estimate for a time-varying radio channel

A method of synchronizing a baseband demodulator in a radio receiver, which may be stationary or mobile. The demodulator is a phase-shift demodulator and detects a baseband signal incoming from a sampling A/D-converter in the receiver. The baseband signal is transmitted from a radio transmitter in the form of bursts, in time slots in accordance with the TDMA-principle. One time slot, in addition to the data word, also includes in a known manner a synchronization part which has a given, fixed bit pattern. Prior to demodulation in the baseband demodulator, differential correlation of the received baseband signal is effected with the known synchronization pattern, wherein a time-dependent correlation function is obtained. The absolute magnitude of the maximum value is calculated and the corresponding time position for this maximum value is detected, which denotes the time position of the synchronization part of the received baseband signal.

Method of synchronizing a radio receiver with an incoming radio signal

Symbol sequences having synchronization sequences are transmitted over a radio channel. Received signals are sampled in signal sampling time points (n) and by correlation a channel response (C.sup.2) is obtained. The impulse response is sampled (T.sub.s) over a period (M.times.N) corresponding to time dispersion of the channel. For separate samples with separate start points (n), channel estimates are obtained (n=0, 2, 4, 6, N=1, 3, 5, 7. . .) whose energy values are calculated, and the estimate (n=8, 10, 12, 14) with the largest energy is selected. The first time point (n=8) in this estimate is selected as sampling time point for the symbol sequence. Alternatively, the signal sampling time point (n=9) with maximum energy value (C.sup.2 max) is selected. By comparing the energy values either one of these signal sampling time points (n=8 , n=9) can be selected as the sampling time point for the symbol sequence. For consecutive sequences, an average value for the sampling time points is calculated.

Method of determining sampling time points

Symbols in a symbol sequence transmitted via a fading channel are estimated in an equalizer having a channel estimating filter. An error signal influences an adaptation circuit which controls adjustable coefficients so as to form a channel estimate, which is adapted during the whole of the symbol sequence. The adaptation circuit performs an adaptation algorithm, which is influenced by mean energy values obtained from the channel estimate in a mean-value-forming circuit. Subsequent to fading the adaptation algorithm is able to control the coefficients so that one of the coefficients will erroneously dominate the channel estimate, with erroneous estimation of symbols as a result. This is counteracted by selecting the largest of the mean energy values, this largest value influencing the adaptation algorithm. When the signal strength of the transmitted symbols falls beneath a threshold value, the coefficient which dominated the channel estimate, for instance the first coefficient is sustained to also dominate after fading and the remaining coefficients are set to zero.

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Stockholm, Sweden

Lars G Larsson