GB2184920A - Cordless telephones - Google Patents
Cordless telephones Download PDFInfo
- Publication number
- GB2184920A GB2184920A GB08601983A GB8601983A GB2184920A GB 2184920 A GB2184920 A GB 2184920A GB 08601983 A GB08601983 A GB 08601983A GB 8601983 A GB8601983 A GB 8601983A GB 2184920 A GB2184920 A GB 2184920A
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- United Kingdom
- Prior art keywords
- channel
- unit
- portable unit
- base unit
- signalling
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/72—Mobile telephones; Cordless telephones, i.e. devices for establishing wireless links to base stations without route selection
- H04M1/725—Cordless telephones
- H04M1/72502—Cordless telephones with one base station connected to a single line
- H04M1/72505—Radio link set-up procedures
- H04M1/72511—Searching for available channels
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Mobile Radio Communication Systems (AREA)
Abstract
A digital cordless telephone is operable in both scanning and call modes. In the scanning mode a control logic means 14 switches both base (4 Fig. 2) and portable 2 units in synchronism to each of a plurality of channels and means 40 monitors the noise or interference level on each channel and provides a "channel" clear signal to to control logic means 14 if the channel is sufficiently free of interference for communication purposes. In the scanning mode the necessary signalling information and synchronisation information is exchanged. In the call mode both portable and base units are tuned to the same channel for establishing a communications link for processing a call using time division multiplexing. <IMAGE>
Description
SPECIFICATION
Cordless telephones
The present invention relates to digital cordless telephone systems, and more particularly, to improvements in the method of operation of such telephones.
A cordless telephone consists of a paired base unit and portable unit. The base unit is connected to a telephone line and the portable unit serves as a handset for making and receiving calls. The portable unit and base unit communicate via a radio link so that the user can make and receive calls at some distance from the base unit.
Existing cordless telephones use analogue communications at fixed frequency between the portable and base units with the link in one direction being at a different frequency from the link in the other direction. In order to reduce interference and allow for larger numbers of users, digital systems have been proposed in which each cordless telephone can use any of a number of channels for digital communications in both directions using timedivision multiplexing. In the U.K. 40 channels of 100 kHz bandwidth have been made available in the 900 MHz band. With such a system it is necessary that both units of the cordless telephone have some system of communicating when a call is not being made in order to detect signals from the other unit indicating that a call has been received or is to be made.
A paper entitled "900 MHz Digital Cordless
Telphone" by P.D. White et al IEE Proceedings, Vol.132, Part F No.5, August 7985, to which reference may be made, describes two proposed options for allocation of a channel for a call. These options can be referred to as 'signalling on the speech channel' and 'signalling on a dedicated channel' In the first option both units continually scan the channels and when one unit wishes to establish communication with the other it stops on a suitable channel and transmits a request to the other unit. When the other unit next reaches that channel during its scan it stops on that channel and a communications link is set up.
In the alternative option a specific channel is set aside for all signalling preparatory to setting up communications link. With this option there may be considerable interference on the signalling channel which would impair operation. A back up signalling channel is usually necessary.
Although the base unit may be mains powered, the portable unit must be battery powered. In order to ensure a maximum operating period when the portable unit is removed from the base unit it is desirable that it should only be powered up periodically for short intervals.
In the case of speech channel signalling this means that it may take a considerable time to scan all the available channels so that there is a significant delay in setting up a communications link.
The option of signalling on the speech channel makes it impossible for a call to be rapidly re-set-up on another channel if communications fail due to interference.
The technical problem of the present invention is therefore to provide a digital cordless telephone which is capable of coping with interference and also allows extended battery life.
The present invention accordingly provides a cordless telephone comprising a base unit and a portable unit, each unit having a radio transmitter and receiver, means for scanning a plurality of predetermined frequency channels and monitoring the interference level on each channel, means for maintaining synchronisation between the scanning means, means for transmitting signalling information on a channel being scanned, means for switching the transmitter from a scanning mode in which the scanning means is operable to a call mode on a fixed channel.
By maintaining the scanning means in both units in synchronism, signalling information can be successfully transmitted to the other unit as rapidly as with systems using a dedicated signailing channel. Moreover, by transmitting the signalling information on successive channels being scanned a successful transmission can rapidly be provided even if the first transmission fails due to interference.
The telephone can also re-establish a communications link if the first channel selected for the call mode becomes subject to interference, by returning to the scanning mode for further signalling to select a new channel. This can be done sufficiently quickly to prevent loss of the call.
Preferably the portable unit is provided with battery economising means which powers up the portable unit for every n th scanning period only, where n and the number of channels are coprime. When the portable unit needs to signal to the base unit, the signalling means of the portable unit is adapted to maintain the power and transmit signalling information on the next channel to be scanned after a normal power-up. When the base unit needs to signal to the portable unit, the signalling means of the base unit is adapted to transmit signalling information only when the portable unit is powered-up. Such an arrangement avoids clashes when both units are trying to establish communications simultaneously, by reserving those scanning periods when the portable unit is powered-up for use only by the base unit as transmitter.
The invention further provides a method of signalling between a base unit and a portable unit of a cordless telephone comprising the steps of tuning the base unit successively to each of a number of predetermined channels for a predetermined scanning period, periodically powering-up the portable unit for a said scanning period and tuning the portable unit to the same channel as the base unit is tuned at that time, transmitting a signalling message from the base unit to the portable unit when a call is received using the channel to which the base unit is tuned at that time, the portable unit maintaining power and changing channels in synchronism with the base unit in response to receipt of a signalling message, the portable unit transmitting a signalling message to the base unit using the channel to which the portable unit is tuned at that time when a call is to be made, the portable unit and the base unit exchanging signalling messages to establish a suitable channel for a communications link and thereafter the base unit and portable unit tuning to said channel.
A cordless telephone embodying the present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which:
Figure 1 is a block diagram of a portable unit of the cordless telephone;
Figure 2 is a block diagram of a base unit of the cordless telephone;
Figure 3 is a timing diagram illustrating the frame structure used for communications between the base unit and the portable unit;
Figure 4 is a diagram for illustrating the operation of the cordless telephone during a call set-up sequence; and
Figure 5 is a diagram for illustrating the operation of the cordless telephone during a call re-establishment sequence.
The portable unit 2 and base unit 4 make up a cordless telephone. The portable unit and base unit are paired and share a common and unique identification number. The base unit 4 is connected to a conventional telephone line 6. Both base unit and portable unit are provided with a digital radio transmitter and receiver which are capable of operation in any of, say, 40 100 kHz channels in the 900 MHz band to transmit a voice signal converted into digital form using any suitable form of modulation e.g. FM, and time division multiplexing.
The portable unit 2 has an antenna 8 connected to an RF filter 10 which is connectable either to a transmitter or receiver via a switch
12 which is controlled by control logic means
14.
A key pad 16 for dialling together with an
"on-hook" switch 18 is provided on the face of the portable unit and provides signals to the control logic means 14. A speaker or earpiece 20 is connected to the output of the receiver and a microphone 22 to the input of the transmitter.
The receiver includes a mixer 24 which
mixes the received RF signal to an IF of, say, 45 MHz. The mixer 24 receives an input from a synthesiser 27, which receives its reference frequency from a crystal oscillator 26 which is accurate to + 10 ppm. The control logic means 14 modifies the synthesiser frequency in dependence on the channel frequency at the input of mixer 24 so that the same IF is produced for every channel. The output of the mixer 24 is fed via a filter 28 to a receiver circuit 30. In a call mode, that is when a communications link is set-up between the base and portable units, the output of the receiver circuit 30 is fed to a demodulator 32 and from there via a buffer 34 to a delta demodulator 36, which converts the digital signal to an analogue signal, which is passed via an amplifier 38 to the speaker 20.
In a scanning or standby mode, when no call is established, the output of the receiver circuit 30 is fed via a threshold detector 40 to the control logic means 14 to provide an indication of the level of noise or interference on the channel. The reference input 42 of the threshold detector 40 is preferably set so that a "channel clear" signal is provided to the control logic means 14 if the channel is sufficiently free of interference for communications purposes.
The transmitter receives an input from microphone 18 which is passed via an amplifier 44 to a delta modulator 46, which converts the voice signal into digitial form. The output of the delta modulator 46 is fed via a buffer 48 which is controlled by the control logic means 14 to output the digital signal to a modulator 50. The output of modulator 50 may be fed either via the synthesiser 27 to a mixer 56, which also receives an input from a crystal oscillator 52 via a switch 54 controlled by the control logic means 14; or the output of the modulator 50 may be fed via the crystal oscillator 52 to the mixer 56. The output of the mixer 56 is fed via an amplifier 58 and switch 12 to the RF filter 10 and antenna 8.
The control logic means 14 are capable of generating signalling messages in response to inputs from the keyboard, and in response to received signalling messages and the channel clear signals. The signalling messages are passed direct to the modulator 50 for transmission.
The base unit 4 shown in Figure 2 is of essentially similar construction to the portable unit 2 and will therefore not be described in detail. Primed reference numerals are used to identify corresponding parts. The principal difference is that the control logic means 14' of the base unit is connected to the telephone line 6 via a hybrid circuit 60 which also couples the receiver output and transmitter input to the line 6 via amplifiers 38' and 44' respectively.
In the call mode the base unit and portable unit communicate on a selected channel using the "ping-pong" principle of time division multiplexing the channel which is described in the paper "900 MHz Digital Cordless Telephone" referred to above. This principle is illustrated with respect to Figure 3. The channel is divided into frames of 2ms duration. In this interval the delta modulator 46 in the transmitter of the portable unit produces 64 bits of speech which are fed to the buffer 48. Half way through the 2ms frame the control logic means 14 outputs 4 bits to the modulator 50.
These 4 bits are followed by the 64 bits of speech from the buffer 48 which are clocked out at approximately twice the input rate to the modulator for transmission. The 4 bits generated by the control logic means 14 include at least one bit of an identity code of the telephone. The code could, for example, consist of 22 bits, allowing at least 4 million users each having a unique code, followed by 12 parity bits for error correction and detection. The whole code would then be transmitted in 34 frames or 68 ms.
In the first half of the portable unit's frame the portable unit receives a similar transmission of 4 signalling bits and 64 voice bits from the base unit. The signalling bits received are passed to the control logic means 14 and the voice bits are expanded by passage through the buffer 34 to the original 2ms frame length. It will be appreciated that operation in the reverse direction is similar.
The control logic means 14,14' match the identification code received and if it is not correct, say three times in succession, the call mode is stopped at that unit and replaced by the scanning mode. This will cause the scanning mode to be re-started at the other unit once a further three identification codes should have been transmitted after the other unit abandoned the call mode and therefore stopped transmitting the identification code on the call channel.
In the scanning mode the base and portable units scan each of the channels in synchronism dwelling on each channel for a fixed scanning period of, say, 40 ms. This is done under the control of the control logic means 14,14' which control the synthesisers 27,27' to make the required channel shifts. The control logic means 14,14' ensure that the two units are time synchronised to within 10 ms so that, when the two units are scanning in step, they coincide on each frequency for at least 20 ms. Normally the portable unit is only powered up for part of the time so that it scans the channels less often. The portable unit is powered up for a scanning period every nth channel where n and the number of channels is coprime. In the present example of 40 channels n may be 9. When powered up the portable unit is scanning the same channel as the base unit.If the portable unit receives signalling information from the base unit when powered up or the user wishes to make a call the control logic means causes the portable unit to remain powered up. This arrangement allows for battery economy yet still allows the control logic means at the portable unit to maintain an up to date status for each of the channels as provided by the receiver circuit 30 and threshold detector 40. In this example the base unit scans all the channels in 1.6 sec while the portable unit requires 9 x 1.6 sec 14.4 sec to scan every channel once.
In order to maintain synchronisation between the units to an accuracy of say 10 ms, the control logic means exchange synchronisation signals at least once every minute. If a prolonged period, say 4m, goes past without receipt of a synchronisation signal a synchronisation mode is initiated. The synchronisation mode is also used to establish synchronisation when the portable unit is first removed from the base unit or is switched 'on' when removed from the base unit.
In the synchronisation mode the portable unit remains fully powered up and scans the channels pseudo-randomly and sends sync requests to the base unit periodically, say every 40 ms. In the synchronisation mode of the portable unit the base unit will be operating in its normal scanning mode so that for 1/40 of the time both units will be operating on the same channel. When the base unit identifies the sync request it transmits a sync signal intermittently as it continues to scan. When the portable unit receives a sync signal it scans from that channel in the normal scanning mode and may also acknowledge the sync signal back to the base unit during the next scanning period to confirm synchronisation has been achieved. The acknowledgement may be sent several times on different frequencies to ensure that it gets through reliably.If half the channels are unusable due to interference the probability of any one sync request being received is 1/80. To ensure a 99% probability of the sync request being received n requests must be made where (1--1/80)" = 0.01 i.e. n = 370. Thus, in this example, a sync request should have been received by the base unit with 99% probability after 370 x 40 ms = 14.8 s.
Alternatively, initial synchronisation may be established by means of a direct connection between the base and portable units which passes synchronisation information before the portable unit is taken from the base unit.
The manner in which the control logic means of either the portable or base units controls the set up of a communications link on a specific channel for processing a call will now be described with reference to Figure 4.
In this example it is assumed that the portable unit initiates the request in order to make a call, but it will be appreciated that a similar process is used by the base unit if a call is received on the telephone line 6.
Initially the base unit scans the channels designated F1,F2,F3 and so on to F40. Since the base unit is powered up all the time, its control logic means 14' sets the base unit to receive and adjusts the synthesiser 27' every 40 ms so that the base unit receiver receives each of the channels F1,F2 etc. for a scanning period of 40 ms. As shown the portable unit is initially powered down for the first two scanning periods but then powers up for the third scanning period and its control logic means 14 adjusts the channel to F3 so that both the base unit and the portable unit are simultaneously tuned to the same channel.
Since there is synchronisation between the units the control logic means 14' at the base unit also stores information as to when the portable unit will be powered up. During some of the scanning periods for which the portable unit is powered up, the base unit transmits a sync signal 70. In this case, the sync signal is transmitted on channel F3. This sync signal is received by the portable unit and can be used by the control logic means 14 to make any necessary fine adjustments of the timing signal for controlling the scanning operation. Since the portable unit is only powered up every 9 scanning periods, it is tuned to channel F12 when it is next powered up.
Now let us suppose that the portable unit wishes is to initiate a call. The control logic means of the portable unit recognises an input from the on-hook switch 1 8 next time it is powered up to channel F21. The control logic means therefore inhibits the periodic powering up sequence and maintains power. A call request signal is transmitted on the next channel, that is F22. Channel F21 is not used in order to avoid clashing with any sync signal or call request being made by the base unit.
In this example we are assuming that channel
F22 is blocked at the base unit. Therefore no acknowledgement signal is received in the next scanning period. The control logic means 14 therefore repeats the output of the signalling message for a call request during the scanning period on channel F24. This repetition of the call request ensures rapid communication with the base unit even though several of the available channels may be blocked. This provides much better performance than cordless telephones which use a dedicated signalling channel as they are incapable of operation if this signalling channel is subject to high levels of interference.
The call request sent by the portable unit includes an indication of a channel for which the control logic means 14 has a channel clear signal stored. In this case, the requested channel is F14. When the base unit receives the call request, it checks whether its control logic means 14' also stores a channel clear signal for the F14 channel. In this case, we assume that it is subject to interference on this channel. Therefore, the acknowledgement signal includes an indication of a channel for which the base unit has a channel clear signal stored. In this case the alternative channel suggested is F36. When this acknowledgement signal is received by the portable unit, the control logic means 14 in the portable unit checks for a channel clear signal on F36. As such a signal is found, the portable unit signals back "go to F36".The base unit acknowledges this signal in the next scanning period and, if the portable unit receives this acknowledgement the control logic means 14 at the portable unit adjusts the tuning of its receiver and transmitter to F36. The base unit does likewise and "ping-pong" communication as explained with reference to Figure 3 can take place on the communications link established on channel F36. It will be appreciated that quite a complex "hand-shaking" procedure can be undertaken between the base unit and the portable unit as they operate in the scanning mode. Once a mutually satisfactory channel is agreed, both base unit and portable unit switch to that channel for handling the call. The exchange of signalling messages and their contents may be varied from the above outline according to design requirements.For example acknowledgement signals may be sent several times on different channels to ensure they get through reliably.
During the course of the call interference may increase on channel F36 at either the base unit or the portable unit so that the identification code is not correctly received by the control logic means of either unit. In such a situation the control logic means can rapidly re-establish the call in a period of typically less than 400 ms. This period is scarcely long enough for the user of the cordless telephone to appreciate the loss in communications. The manner in which call re-establishment is carried out will be described with reference to
Figure 5.
In the example shown in Figure 5 it is assumed that the interference at the portable unit on channel F36 becomes sufficiently high to prevent correct receipt of the identity code.
When three erroneous identity codes have been received by the control logic means 14 of the portable unit, the portable unit switches from call mode to the scanning mode. The control logic means 14 maintains an internal clock so that the next channel to be scanned is the channel that would have been scanned if the portable unit had stayed in scanning mode instead of switching to call mode. In this case the next scanning mode channel is assumed to be F16. The portable unit then sends signalling messages requesting the base unit to re-establish the call on a particular channel which the portable unit has a channel clear signal for. In this case the new channel requested is F19. The re-establish call signalling message 74 is sent periodically. Here, we show it being sent in channels F17, F27 and
F3.
The base unit, as shown in Figure 5, remains in the call mode until it also receives three erroneous identity codes. This will normally take place in the time interval for which three identity codes should have been transmitted after the portable unit switched from the call mode to the scanning mode.
Once the base unit switches from call mode to scanning mode it starts scanning at the next scanning period in sequence and is therefore automatically tuned to the same channel as the portable unit is tuned to at that time.
In this case the base unit joins the scanning mode at channel F2, therefore, the next time the re-establish call signalling message 74 is sent by the portable unit on channel F3, it is received by the base unit, which then sends an acknowledgement signal during the next scanning period. In this example, it is assumed that channel F19 is also clear at the base unit and this information is contained in the acknowledgement signal. On receipt of the acknowledgement signal the portable unit and the base unit both switch to channel F19 and resume the call mode.
All the control messages generated by the control logic means of this system, for example, the sync signals, the call request signal and acknowledgement signals, each have a duration of typically 1 to 2 ms at a transmission rate of 70kb/s. In the scanning mode the guaranteed overlap time between the portable unit and base unit on each channel is 20 ms.
Allowing 10 ms for frequency synthesiser switching, the remaining 10 ms is available for the control message which could be pseudorandomly timed within that period to help reduce clashes with other users.
When the telephone is operating in the scanning mode, it is necessary for the control logic means to be able to distinguish between control signals and voice transmissions by other users on a channel. Only the latter should be used in assessing the status of the channels by means of the threshold detector 40. The control signals can be distinguished from voice transmissions by taking a number of samples of the signal strength on the channel, say one per ms, and looking for signals which exist for most of the dwell on the channel.
The foregoing discussion has assumed that the identity code is fixed for a given base unit portable unit pair. An alternative is to have a fixed and variable part of the identity code. The variable part may be determined by a counter, or pseudo-random generator, which advances while the portable unit is physically connected to the fixed unit, but stops advancing at the instant when the physical connection is broken, thus giving a randomised variable part of the identity code which is the same for both units.
It will be appreciated that the described time synchronised signalling used by this cordless telephone is readily capable of adapting to the interference environment since no specific channel is used for all the signalling. It also provides excellent scope for battery economy as the portable unit can be powered down for eight out of every nine scanning periods. The duty cycle of the powering of the portable unit can readily be adjusted according to the battery economy required provided all the channels are scanned within a reasonable period. A further advantage of the described cordless telephone is its ability to reestablish calls if the channel servicing the communications link is subject to interference.
The improved performance of the described cordless telephone can be obtained with a very small traffic overhead for the required signalling and for maintaining synchronisation.
The numeric parameters above are given by way of example only and are not intended to be restrictive in any way. Also, although delta modulation has been specified above, any other form of speech digitisation could be equally well employed. Alternatively the speech could be kept in analogue form and merely time compressed for the ping-pong transmission.
Claims (10)
1. A cordless telephone comprising a base unit and a portable unit, each unit having a radio transmitter and receiver, means for scanning a plurality of predetermined frequency channels and monitoring the interference level on each channel, means for maintaining synchronisation between the scanning means of the base unit and the portable unit, means for transmitting signalling information on a channel being scanned, and means for switching the transmitter and receiver from a scanning mode in which the scanning means is operable to a call mode on a fixed channel.
2. A cordless telephone according to claim 1, wherein the portable unit is provided with battery economising means which powers up the scanning means of the portable unit for every n th scanning period of the base unit, where n and the number of channels are coprime.
3. A cordless telephone according to claim 2, wherein the portable unit comprises means for indicating to its transmitting means when a call is to be made, the signalling means of the portable unit being adapted, in response to such an indication, to maintain the power and transmit signalling information on the next channel to be scanned after a normal power up.
4. A cordless telephone according to claim 2 or 3, wherein the signalling means of the base unit is adapted to transmit signalling information only when the portable unit is powered up.
5. A cordless telephone according to any one of the preceding claims, wherein the signalling means of each unit is connected to the interference level monitoring means such that the signalling information transmitted indicates whether the interference level on a channel identified by the other unit is acceptable or the identity of a channel on which the interference level is acceptable when a call is to be connected between the units.
6. A cordless telephone according to any one of the preceding claims, wherein the switching means is adapted to switch the transmitter and receiver from a call mode back to the scanning mode in response to a failure of the call.
7. A method of signalling between a base unit and a portable unit of a cordless telephone comprising the steps of tuning the base unit successively to each of a number of predetermined channels for a predetermined scanning period; on initially powering up, the portable unit scanning the channels pseudorandomly and transmitting sync requests periodically, the base unit transmitting sync signals while scanning the channels in response to receipt of the sync request in order to enable the portable unit to achieve synchronisation with the base unit, thereafter periodically powering-up the portable unit for a said scanning period and tuning the portable unit to the same channel as the base unit is tuned at that time, transmitting a signalling message from the base unit to the portable unit when a call is received using the channel to which the base unit is tuned at that time, the portable unit maintaining power and changing channels in synchronism with the base unit in response to receipt of a signalling message, the portable unit transmitting a signalling message to the base unit using the channel to which the portable unit is tuned at that time when a call is to be made, the portable unit and the base unit exchanging signalling messages to establish a suitable channel for a communications link and thereafter the base unit and portable unit tuning to said channel.
8. A method according to claim 7, wherein during communications between the base unit and the portable unit on a fixed channel, signalling bits are exchanged between the units in addition to the message bits, said signalling bits being set to represent an identification code which is unique to a cordless telephone, either unit being adapted to return to successively scanning channels if the identification code is incorrectly received a predetermined number of times in succession.
9. A cordless telephone substantially as herein described with reference to the accompanying drawings.
10. A method of signalling between a base unit and a portable unit of a cordless telephone substantially as herein described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB858531492A GB8531492D0 (en) | 1985-12-20 | 1985-12-20 | Cordless telephones |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8601983D0 GB8601983D0 (en) | 1986-03-05 |
| GB2184920A true GB2184920A (en) | 1987-07-01 |
| GB2184920B GB2184920B (en) | 1990-01-10 |
Family
ID=10590105
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB858531492A Pending GB8531492D0 (en) | 1985-12-20 | 1985-12-20 | Cordless telephones |
| GB8601983A Expired - Fee Related GB2184920B (en) | 1985-12-20 | 1986-01-28 | Cordless telephones |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB858531492A Pending GB8531492D0 (en) | 1985-12-20 | 1985-12-20 | Cordless telephones |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8531492D0 (en) |
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0298674A2 (en) * | 1987-07-07 | 1989-01-11 | Libera Developments Limited | Digital Communication Systems |
| GB2187065B (en) * | 1986-02-21 | 1990-04-04 | American Telephone & Telegraph | Computer-controlled cordless telephone |
| EP0448197A2 (en) * | 1990-02-17 | 1991-09-25 | Gec Plessey Telecommunications Limited | Cordless telecommunications apparatus |
| EP0454080A2 (en) * | 1990-04-24 | 1991-10-30 | Nec Corporation | Cordless telephone system capable of quickly establishing connection during call setup phase |
| EP0494461A2 (en) * | 1991-01-08 | 1992-07-15 | Thomson Consumer Electronics, Inc. | Automatical channel selection system for a cordless telephone |
| GB2260882A (en) * | 1991-10-21 | 1993-04-28 | American Telephone & Telegraph | A cordless telephone arranged for operation in a frequency hopping system |
| WO1995019084A1 (en) * | 1994-01-05 | 1995-07-13 | Thomson Consumer Electronics, Inc. | Clear channel selection system for a cordless telephone |
| GB2285723A (en) * | 1994-01-18 | 1995-07-19 | Motorola Ltd | Direct TDMA communication between mobiles |
| GB2271487B (en) * | 1992-10-09 | 1995-08-02 | Maxon Systems Inc | Single antenna transmitter/receiver |
| FR2724085A1 (en) * | 1994-07-30 | 1996-03-01 | Motorola Ltd | TELECOMMUNICATIONS METHOD AND DEVICE PROVIDING ADAPTIVE TEMPORAL POSITIONING OF SALVES TRANSMISSION |
| WO1998044700A1 (en) * | 1997-03-27 | 1998-10-08 | Northern Telecom Limited | Cordless telephone programming and configuration |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1185789A (en) * | 1967-08-11 | 1970-03-25 | Cit Alcatel | Transreceivers |
| EP0171071A2 (en) * | 1984-08-07 | 1986-02-12 | Nec Corporation | Radio communication system comprising a portable unit carrying out a battery saving operation related to a scanning operation of a fixed unit |
| EP0200209A2 (en) * | 1985-04-30 | 1986-11-05 | Nec Corporation | Cordless telephone apparatus having means for synchronizing channel scanning of fixed and portable units |
-
1985
- 1985-12-20 GB GB858531492A patent/GB8531492D0/en active Pending
-
1986
- 1986-01-28 GB GB8601983A patent/GB2184920B/en not_active Expired - Fee Related
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1185789A (en) * | 1967-08-11 | 1970-03-25 | Cit Alcatel | Transreceivers |
| EP0171071A2 (en) * | 1984-08-07 | 1986-02-12 | Nec Corporation | Radio communication system comprising a portable unit carrying out a battery saving operation related to a scanning operation of a fixed unit |
| EP0200209A2 (en) * | 1985-04-30 | 1986-11-05 | Nec Corporation | Cordless telephone apparatus having means for synchronizing channel scanning of fixed and portable units |
Cited By (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2187065B (en) * | 1986-02-21 | 1990-04-04 | American Telephone & Telegraph | Computer-controlled cordless telephone |
| EP0298674A3 (en) * | 1987-07-07 | 1990-05-02 | Libera Developments Limited | Digital communication systems |
| EP0298674A2 (en) * | 1987-07-07 | 1989-01-11 | Libera Developments Limited | Digital Communication Systems |
| EP0448197A2 (en) * | 1990-02-17 | 1991-09-25 | Gec Plessey Telecommunications Limited | Cordless telecommunications apparatus |
| EP0448197A3 (en) * | 1990-02-17 | 1993-04-14 | Gec Plessey Telecommunications Limited | Cordless telecommunications apparatus |
| EP0454080A2 (en) * | 1990-04-24 | 1991-10-30 | Nec Corporation | Cordless telephone system capable of quickly establishing connection during call setup phase |
| EP0454080A3 (en) * | 1990-04-24 | 1993-04-14 | Nec Corporation | Cordless telephone system capable of quickly establishing connection during call setup phase |
| EP0494461A2 (en) * | 1991-01-08 | 1992-07-15 | Thomson Consumer Electronics, Inc. | Automatical channel selection system for a cordless telephone |
| EP0494461A3 (en) * | 1991-01-08 | 1993-03-03 | Thomson Consumer Electronics, Inc. | Automatical channel selection system for a cordless telephone |
| GB2260882A (en) * | 1991-10-21 | 1993-04-28 | American Telephone & Telegraph | A cordless telephone arranged for operation in a frequency hopping system |
| GB2260882B (en) * | 1991-10-21 | 1995-12-13 | American Telephone & Telegraph | Method of initiating, and arrangement for providing communication between a base unit and a handset unit |
| GB2271487B (en) * | 1992-10-09 | 1995-08-02 | Maxon Systems Inc | Single antenna transmitter/receiver |
| WO1995019084A1 (en) * | 1994-01-05 | 1995-07-13 | Thomson Consumer Electronics, Inc. | Clear channel selection system for a cordless telephone |
| US6041240A (en) * | 1994-01-05 | 2000-03-21 | Thomson Consumer Electronics Inc. | Clear channel selection system for a cordless telephone |
| GB2285723A (en) * | 1994-01-18 | 1995-07-19 | Motorola Ltd | Direct TDMA communication between mobiles |
| GB2285723B (en) * | 1994-01-18 | 1997-09-10 | Motorola Ltd | Communications system |
| FR2724085A1 (en) * | 1994-07-30 | 1996-03-01 | Motorola Ltd | TELECOMMUNICATIONS METHOD AND DEVICE PROVIDING ADAPTIVE TEMPORAL POSITIONING OF SALVES TRANSMISSION |
| DE19526549B4 (en) * | 1994-07-30 | 2007-04-05 | Motorola Ltd., Basingstoke | Communication device and method with adaptive burst transmission time |
| WO1998044700A1 (en) * | 1997-03-27 | 1998-10-08 | Northern Telecom Limited | Cordless telephone programming and configuration |
| US6212396B1 (en) | 1997-03-27 | 2001-04-03 | Nortel Networks Limited | Generic handset programming and configuration |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8531492D0 (en) | 1986-02-05 |
| GB8601983D0 (en) | 1986-03-05 |
| GB2184920B (en) | 1990-01-10 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |