Low-power frequency-hopped spread spectrum acknowledgement paging system

• US 5,499,266 A
• Filed: 12/22/1994
• Issued: 03/12/1996
• Est. Priority Date: 08/20/1992
• Status: Expired due to Fees

• Current Assignee: Nexus 1994 Limited
• Original Assignee: Nexus 1994 Limited
• Inventors: Harel, Haim, Meiman, Yehouda, Yokev, Hanoch
• Primary Examiner(s): CANGIALOSI, SALVATORE A
• Application Number:
  US08/362,794
• Time in Patent Office: 446 Days
• Field of Search: 375/1, 375/56, 375/202, 370/59, 370/95.1
• US Class Current: 375/136
• CPC Class Codes: G01S 1/026 of associated receivers
• CPC Class Codes: G01S 3/023 Monitoring or calibrating
• CPC Class Codes: G01S 3/043 Receivers
• CPC Class Codes: G01S 3/10 Means for reducing or compensating for quadrantal, site, or like errors
• CPC Class Codes: G01S 5/0009 Transmission of position information to remote stations involving assistance data G01S5/0236
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: H04B 1/713 using frequency hopping
• CPC Class Codes: H04B 1/7156 Arrangements for sequence synchronisation
• CPC Class Codes: H04B 7/2681 Synchronisation of a mobile station with one base station
• CPC Class Codes: H04B 7/2693 Centralised synchronisation, i.e. using external universal time reference, e.g. by using a global positioning system [GPS] or by distributing time reference over the wireline network
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0053 Allocation of signaling, i.e. of overhead other than pilot signals
• CPC Class Codes: H04L 5/0062 Avoidance of ingress interference, e.g. ham radio channels
• CPC Class Codes: H04L 5/0091 Signaling for the administration of the divided path
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management
• CPC Class Codes: H04W 84/025 with acknowledge back capability
• CPC Class Codes: H04W 88/022 Selective call receivers
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

An acknowledgement paging system is described which fits within the existing infrastructure of a paging network and which provides low cost manufacture and low power operation while still enabling the acknowledgement paging over long distances. The acknowledgement paging system consists of a standard paging transmitter and a plurality of remote paging units which respond to a page using frequency-hopped spread-spectrum differential bi-phase shift keying communications. The plurality of pagers are assigned to groups with each group being assigned a separate starting location in a common, repeating pseudo-random noise code which determines the frequency hops. The grouping of pagers minimizes the collisions of acknowledgment transmissions between groups and the enables a large number of paging units to operate within a single geographic area. The pagers include a special double loop PLL synthesizer to produce an accurate narrow band frequency and to change or hop frequencies in a rapid fashion. The base receiving unit employs special algorithms for retrieving very low power acknowledgement paging messages in a noisy environment by using data redundancy, data interleaving, soft decoding and error correction codes to strip the bi-phase-modulated, frequency-hopped spread-spectrum digital data transmitted from the remote pocket pagers. A history of the frequency and phase drift is used during reception of the acknowledgement messages to predict the phase and frequency drift of the encoded digital information to further reduce decoding error. Signal to noise ratios are determined for each frequency hop and relatively noisy hops are discarded or minimized in a soft decoding process based redundancy of data bits.

Claims

1. A base receiver for use with a reverse paging system having a base transmitter for transmitting pager uplink messages in one of a plurality of paging channels each corresponding to unique addresses and a plurality of remote units for receiving the messages and transmitting downlink information using frequency-hopped spread-spectrum radio frequency signals synchronized to a repeating pseudo-random code sequence, the base receiver comprising:

clock means for producing a local repeating pseudo-random code sequence in synchrony with the repeating pseudo-random code sequence of the remote units;

radio frequency receiving means connected to the clock means for simultaneously receiving a plurality of downlink frequency-hopped spread-spectrum radio frequency signals from the plurality of remote units;

down converter means connected to the radio frequency receiving means for separating the downlink frequency-hopped spread-spectrum radio frequency signals into a plurality of narrow-band frequencies corresponding to assigned frequency hops and for downconverting the plurality of narrow-band frequencies corresponding to the assigned frequency hops for producing therefrom a plurality of downconverted frequency hops;

decoding means connected to the down converter means and the clock means and operable for decoding information contained in each of the downconverted frequency hops to track the frequency hops of at least one of the plurality of remote units in synchrony with the local repeating pseudo-random code sequence; and

control means connected to the down converter means, connected to the clock means and connected to the decoding means, the control means operable for selecting the local oscillator frequencies needed for downconverting the plurality of narrow-band frequencies corresponding to the assigned frequency hops.

2. The base receiver according to claim 1 wherein the decoding means further includes means for decoding phase shift keying modulation of the frequency hops to produce therefrom a plurality of data bits from each of the frequency hops.

3. The base receiver according to claim 2 wherein the decoding means further includes means for tracking the phase drift of the phase shift keying modulation of the frequency hops to assist in accurate decoding of the data bits from each of the frequency hops.

4. The base receiver according to claim 2 wherein the decoding means comprises a plurality of processing pipelines, each of said pipelines operable for downconverting a portion of the plurality of narrow-band frequencies corresponding to the assigned frequency hops of a portion of the plurality of remote units.

5. The base receiver according to claim 4 wherein each of the plurality of processing pipelines comprises at least one digital signal processor for simultaneous demodulation of a plurality of narrow-band carrier frequencies by performing a Fourier Transform.

6. A base receiver for use with a reverse paging system having a base transmitter for transmitting messages each corresponding to unique addresses and a plurality of remote units for receiving the messages and transmitting information, the base receiver comprising:

radio frequency receiving means for receiving frequency-hoped spread-spectrum radio frequency signals from the plurality of remote units;

down converter means connected to the radio frequency receiving means for downconverting the frequency-hopped spread-spectrum radio frequency signals and for producing therefrom a plurality of frequency hops;

decoding means connected to the down converter means for decoding information contained in each of the frequency hops and for decoding modulation of the frequency hops to produce therefrom a plurality, of data bits from each of the frequency hops;

control means connected to the down converter means and the decoding means for selecting the local oscillator frequencies needed for downconverting the frequency-hopped spread-spectrum radio frequency signals;

wherein the decoding means is further operable for performing the steps of;

determining the signal to noise ratio of each of the frequency hops;

de-interleaving the plurality of data bits from each of the frequency hops;

locating individual bits of the plurality of data bits from each of the frequency hops to produce redundant groups of encoded bits of digital data;

tabulating the redundant groups of encoded bits of digital data to produce a table of a plurality of values representing the individual groups;

weighting each entry in the table of the plurality of values representing the individual groups by the signal to noise ratio of each of the hop frequencies to which each individual bit corresponds to produce weighted values for each of the individual bits; and

decoding the digital value of each of the weighted values for each of the individual bits.