Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Patent
1998-06-26
2000-11-07
Vo, Don N.
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
375150, H03D 100, H04L 2706
Patent
active
061447099
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method of detecting a call set-up burst in a digital radio system in which a call is set up in a predetermined time slot by a certain call set-up burst which comprises a known training sequence; in the method, the position and energy of the maximum point of an impulse response in a time slot are estimated by correlating a sampled, received signal with a known training sequence and by computing the average energy of the maximum point of the impulse response per one correlation result.
BACKGROUND ART
The present invention can be applied in digital radio systems in which subscriber equipments send a specific call set-up message when they want to establish a radio connection with a base station and in which the call set-up message comprises a training sequence. Typically, a call set-up message is sent on a random access channel, which means that message transmission does not have an exact predetermined starting and ending moment. It is typical of a random access channel that transmissions on the channel may coincide and so a transmission may have to be repeated. The base station does not know when the terminal equipments need to communicate, and so it cannot allocate them turns to transmit beforehand.
Detection of a call set-up message at a base station is demanding, since the base station does not know beforehand the moment when a signal will arrive, the power level of the signal, or its possible frequency deviation from the nominal frequency of the call set-up channel. To facilitate detection of a message, the message usually contains a number of previously known bits, a sequence of previously known bits being called a training sequence. A training sequence is commonly used in digital radio systems, since it can be used in computing the properties of the channel, such as an impulse response, by which one can attempt to correct any distortions that the channel may cause in a signal.
In prior art solutions, a decision whether or not a signal received in a given time slot comprises a call set-up message is made after an equalizer when an decoded assumed training sequence is compared with a known training sequence. If there are many error bits, the signal has probably contained noise rather than a message. Call set-up should be rendered as quick and reliable as possible, since this adds to user comfort. The quicker a call set-up message can be detected, the quicker a call can be set up between a base station and a terminal equipment.
DESCRIPTION OF THE INVENTION
The object of the present invention is to provide a method by which a call set-up message can be detected earlier than before. The method provided by the invention is also reliable, and it can be used either as such or in combination with other methods.
The object is achieved by a method described in the introduction, the method being characterized by averaging the energy contained in the correlation results of the other samples of the time slot per one correlation result, computing the ratio between the averaged maximum energy of the impulse response and the average energy of the other samples of the time slot, and if the ratio is higher than a given threshold, deciding that a call set-up burst was received in the time slot concerned.
The invention also relates to a receiver of a digital radio system, the receiver comprising a converter for sampling a signal received in a given time slot, means for correlating digitalized samples with a known training sequence, and means for computing the energy of the correlation results obtained, means for looking for the maximum values of a string of samples of a given order from the computed energies, and means for averaging the maximum values found per one sample. The receiver provided by the invention is characterized in that the receiver comprises means for averaging the energy of the other samples of the time slot per one sample, and means for comparing the averaged maximum energy values with the energy values of the other samples.
The method of the invent
REFERENCES:
patent: 5228057 (1993-07-01), Larsson
patent: 5373507 (1994-12-01), Skold
patent: 5838672 (1998-11-01), Ranta
patent: 5912932 (1999-06-01), Calderbank et al.
patent: 5917856 (1999-06-01), Torsti
Jyrkka Kari
Piirainen Olli
Nokia Telecommunications Oy
Phu Phoung
Vo Don N.
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