MXPA00005714A - Power saving protocol for tdma multi-line wireless telephone handsets - Google Patents

Abstract

A wireless telephone system comprises a base unit having a base transceiver, and one or more wireless handsets, each handset comprising a handset transceiver. Each handset establishing a time-division multiple access (TDMA) link over a shared RF channel with the base unit via the base transceiver in accordance with a TDMA epoch, which allocates exclusive data and audio packet time slots to each handset. Each handset powers on its transceiver during its respective data and audio packet time slots as necessary to synchronize with the base unit using synchronization data transmitted with a data packet, to detect incoming call data transmitted with a data packet, or to transmit and receive audio information over the TDMA link. The handset powers off its transceiver otherwise during the epoch to minimize handset power use.

Description

ENERGY SAVING PROTOCOL FOR WIRELESS TELEPHONE HEADPHONES OF MULTIPLE TDMA LINES (MULTIPLE ACCESS OF TIME DIVISION) BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to multi-line cordless telephone systems, and in particular, to energy-saving techniques in cordless handsets operated by battery in wireless telephone systems.

Description of the Related Art The use of telephones and telephone systems, including wireless telephone systems, is widely spread. In wireless telephone systems, a wireless telephone headset unit communicates via analog to digital radio signals with a base unit, which is normally connected via a conventional telephone line to an external telephone network. In this way, a user can use the wireless headset to engage in a telephone call with another user, through the base unit and the telephone network. Multi-line wireless telephone systems are also being used in different situations, such as business with many phone users. These systems employ a headset that communicates with up to N headphones in a simultaneous manner, typically with digital communication schemes, such as extended-spectrum time division multiple access (TDMA). In a TDMA system, a single radio frequency channel is used, and each headset transmits and receives data during a dedicated slot or time slot within a cycle or global time. It is important an efficient use of energy for a wireless system, because the headphones are usually powered by battery. The above energy saving configurations, and other TDM type configurations for battery powered devices, are described in U.S. Patent No. 4,964,121 (Moore), issued October 16, 1990; in U.S. Patent No. 5,150,361 (Wieczorek et al.), issued September 22, 1992; and in European Patent Application Number EP-0,726,687 Al (Nokia Mobile Phones Ltd.), published on August 14, 1996. The Moore patent describes a TDM system in which the communication channel is divided into a predetermined number of communication channels. time slots, wherein a remote communication unit can communicate with a central control station within an assigned time slot. Moore describes individual radios battery saving circuits that can monitor in a synchronized manner the centrally transmitted synchronization signals in their respective predetermined assigned time slots, but otherwise, is in a substantially non-energy saving operating mode. energized The Wieczorek et al. Patent discloses a TDM system wherein the battery-powered communication devices operate in energy saving mode to deactivate the non-essential circuits during a predetermined time interval, waking up to monitor one of two control slots of a repetitive time frame structure. The Nokia reference describes a radiotelephone system, wherein the telephone can be placed in an active condition during a cluster burst, but is in sleep condition at other times.

COMPENDI A wireless telephone system comprises a base unit having a base transceiver, and one or more wireless headsets, each headset comprising a headset transceiver. Each handset establishes a time division multiple access (TDMA) link on a radio frequency channel shared with the base unit by means of the base transceiver according to a time of TDMA, which allocates data packet time slots and exclusive audio to each headset. Each headset energizes its transceiver during its respective data packet and audio time slots as necessary to synchronize with the base unit using the synchronization data transmitted in a data packet., to detect the data of the incoming call transmitted with a data packet, or to transmit and receive audio information on the TDMA link. The headset deactivates its transceiver in another way during the era to minimize the use of headphone power.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a multi-line TDMA wireless telephone systems, in accordance with one embodiment of the present invention. Figure 2 is a schematic representation of the TDMA slot structure and the handset counters used in the TDMA scheme of the system of Figure 1, in accordance with one embodiment of the present invention. Figure 3 is a state diagram of the energy saving protocol implemented by each handset of the telephone system of Figure 1, in accordance with one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED MODE Referring now to Figure 1, a block diagram of a multi-line wireless telephone system TDMA 100 is shown, in accordance with one embodiment of the present invention. The TDMA system 100 comprises a base unit 110, which has receiver and transmitter units 112 and 111, respectively, and is coupled to the external telephone network 116 via the telephone lines 115. The system 100 also comprises N wireless headphones 120! , 1202, ... 120N. Each does not have a transmitter and receiver unit (transceiver), such as transmitter 121 and receiver 122 of earphone 120-L. At any given time, some number (or none) of the headphones are operating or off-hook (ie, in the process of conducting a telephone call). Accordingly, the system 100 provides a wireless network between the base station 110 and each headset 120. ^ (l <i> N). In one embodiment, the system 100 comprises 4 headphones 1201-1204, all of which may be active in a simultaneous manner. In another embodiment, the system 100 comprises a different number of headphones, for example N = 12, of which up to 8 may be active or operational at the same time. As explained above, the efficient use of energy is important for a wireless telephone system, because the headphones are usually battery powered. Accordingly, in one embodiment, the present invention comprises a TDMA system and protocol for connecting multiple transceivers to a base station on a single radiofrequency channel. In particular, the system 100 employs a digital TDMA scheme, as described in more detail below, which allows energy to be used efficiently, because each operating headset is "off" (ie, it is not transmitting or receiving data). , and therefore, is not using as much battery power) during most portions of the TDMA era, and is only "on" during its own slices or time slots, as described in more detail below. In one embodiment, a headset is turned off by switching the power off to at least its CPU and transceiver unit (receiver and transmitter), while leaving only one clock and its associated timer or sequence controller circuit energized, sufficient to wake the CPU and a predetermined time slot. However, the use of a time division multiplexing (TDM) technique, such as TDMA, and the activation of each transceiver (atrial) only during its own time slots, can give rise to different problems. For example, because the headphones use a radio frequency energy detector to detect when a signal is being transmitted from the base station 110 to one of the headphones, the intended communication for a headset can activate other headphones, causing unnecessary draining of the headphones. the battery in those other headphones. In the present invention, therefore, the headphones are carefully synchronized, such that each headset only "hears" the transmissions in their own time slots. Without the present invention, there may be a tendency for the local time bases of the headphones to become out of phase with time, which could result, after a period of time, that each headset will listen to all the transmissions, to resynchronize the base unit 110. After this synchronization, the headset could once again only listen in its time slot. However, because "listening" requires energy, when synchronization is lost, there will be a wasted use of battery power. In addition, if synchronization is lost, link integrity may be lost, due to the signal collision, which occurs when multiple devices try to use a single radio frequency channel at the same time. Accordingly, each headset 121i employs the protocol of the present invention, as described in more detail below, to allow this on and off to occur, without losing synchronization. The synchronization protocol of the present invention allows each independent remote headset to use the local time bases to synchronize with the TDMA sequence from the base station, synchronizing in certain transmissions from the base, and then listening only in the appropriate time slot. Referring now to Figure 2, there is shown a schematic representation of the TDMA slot structure 250 and the headphone counters 210 used in the TDMA scheme 200 of the system of Figure 1, in accordance with one embodiment of the present invention. The system 100 employs a TDMA epoch having the structure 250, which is illustrated by assuming 12 total headphones 120-L-120-L2 of which 8 can be active or operative at the same time, for example the headphones 1201-1208. The TDMA 250 period structure comprises a number of rows and columns. Each row of the structure TDMA 250 represents a field of 2 milliseconds of digital data, and is par or non, and is grouped in a pair with a row or field non or pair, respectively. The TDMA 250 era structure is a 48 millisecond time period. Each field of digital data comprises nine packets in total: a packet of data in the first column (either transmitted from the base or from an earphone), and eight audio packets, grouped in 4 pairs of two. Each pair of audio packets in a row includes a packet (time slot) of the audio transmission from the base (to a given handset from the base unit 110), and an audio transmission packet from the handset (from the handset) given to the base). Each data packet is a set of data transmitted either to a given handset from the base unit, or vice versa during a separate time slot during which time no other handset receives or transmits data on the system data channel. These data packets may contain different types of data, such as data or synchronization words with time stamp information transmitted to a handset in sleep mode, caller identification information, incoming call information, and Similar. Data packets transmitted from a handset to the base may contain information, such as the telephone number that is being dialed by the handset. Each audio packet is a set of audio data transmitted either to a given handset from the base unit, or vice versa, during a time slot given in the global time period again during which time no other handset receives or transmits data about it. only radio frequency channel of the system. Therefore, for example, the pair of rows 0 comprises an even row and a non row. In the even row, the base transmits data in the first time slot (slot 251), to one of the twelve headphones, for example the headset 12 Q1. There are a couple of rows at time 250 for each handset, so that each handset can receive and transmit data to the base unit 110, once per time. After the first data slot 251, assuming the 120-L headset is operational (off-hook), an audio packet is transmitted to the headset 120 in the audio pack slot 253, then an audio packet is transmitted through the headset 120! to the base unit 110 in the audio pack slot 254, and so on for the other 3 headphones to the end of the field or row. In the non row for the pair of rows 0, the data slot 252 is used to receive the data transmitted from the headset 120-L to the base unit 110, and audio packets are transmitted for the remaining 8 active headsets. In the pairs of rows 1-11, the same sequence occurs, except that the data packets are to and from different headphones than to the pair of rows 0. In the present invention, a time base capable of solving a fraction is established of a time slot during the period of several seconds in each handset, which matches the time of the TDMA slot in the base unit 110. The TDMA 250 time structure is known both for each handset and for the base, and once When the time bases are synchronized, the headset receiver will know when to listen to the transmissions from the base, and will know when to send data back to the base. Maintaining the known TDMA slots to within microseconds for a 1 second interval requires that a very stable and accurate reference be provided to operate this time base. To eliminate protocol collisions, all headsets are given a designated data time slot, and the audio time slots are assigned dynamically, according to how the headset needs them. This information is communicated on the data channel (the first column of the TDMA 250 structure). The TDMA slots are divided into data and audio slots in a two-dimensional configuration, as illustrated in Figure 2. The base transmits the synchronization packets to the headphones in their respective data slots until a call is initiated. Each handset maintains a cascade of counters 210, to prevent the local time of each handset from being entrained, and therefore, in synchronization with the TDMA sequence. This is done by applying a reference clock signal to the first counter 211 (all counters are initialized at some previous point, whose initialization can proceed in stages). The reference clock signal is provided by a local clock in the handset, which is adjusted periodically as necessary, to correct the drag, according to the time stamp synchronization information transmitted by the base unit 110 during the time slots. the data packages. The counter 211 keeps track of the resolution of sub-packets, and identifies which bit of the packet is being processed, starting, for example, 100 bits per audio packet. Counter 212 maintains the track of the horizontal packet, or time slot (i.e., the column number of the current row or field of the TDMA 250 time structure). The counter 213 keeps track of whether the current row is non or even, and the counter 214 keeps track of whether or not the current packet is a packet of data, and with which handset the data packet is correlated, and if the data packet is to or from the base unit 110. Finally, the counter 215 keeps track of what time the system 100 is at. This may be useful to request retransmission of corrupt data sent by the base unit 110 during certain epoch, for example. The TDMA system of the present invention saves energy by deactivating most of the components of the handset, other than the internal clock and the sequence controller circuit, for most of the TDMA time. However, the internal clock and the protocol implemented by each headphone ensures that synchronization is not lost, even when the handset is de-energized. Therefore, energy is saved, but synchronization is not lost. Each headset can be in one of two states: in sleep mode, or in the operating mode. In sleep mode, when the handset is hung, only an internal clock and a sequence controller clock run for most of the time, where the clock has been previously synchronized with the clock and the time of the base unit. Therefore, in the sleep mode, the handset is configured in such a way that it wakes up and "hears" the data during its assigned "receive data" slot, and switches off again later, if there is no incoming call. The awakening is caused by the chronometer of the sequence controller that counts down to a certain value, which activates the CPU and other components necessary to listen and / or transmit data. During this data slot, the handset receives the synchronization data from the base unit 110, and adjusts its internal clock, if necessary, to correct any phase shifts. In the next data slot, the handset can wake up again to recognize that it is alive and in sync, by transmitting an "I am alive" data message suitable to the base unit 110. Therefore, in a mode, when it is in the mode of sleeping, each headset is activated only by two data packets of all time TDMA, a duty cycle of approximately 0.93 percent (2 slots / (9 x 12 x 2 slots)). The energization to allow the handset to listen to the transmission of a data packet from the base unit 110 once each 48 millisecond period is sufficient to allow a handset to remain synchronized (i.e., to keep communication cycles secured), and also to allow any incoming calls to be detected sufficiently quickly in order to alert the user to incoming calls (for example, to allow the identification information of the caller to be seen, and / or calls to be answered). in real time) . In an alternative mode, the handset jumps a number of times entirely, and, for example, wakes up during its data slots only once during every third epoch, because this will also be sufficient for synchronization and real-time monitoring of the incoming call. This reduces the work cycle additionally. The "I am alive" message from the handset (e.g., transmitted in data slot 252) does not need to be transmitted every epoch, or even every epoch when the handset wakes up and listens to the data from the base unit 110. Preferably, These parameters are programmable by the user. For example, a headset can be programmed to wake up every third time and listen during its data slot, and to transmit back a message of "I am alive" every sixth time. In this case, the base unit, which does not have similar power limitations, will nevertheless transmit the synchronization data each time, but will know that the headset is properly synchronized, as long as a "I am alive" data message is received every six epochs Otherwise, the base unit 110 can assume that the insurance has been lost, and can then try to reestablish the link, for example, by transmitting data packets / synchronization to the lost handset at three increasing power levels, during its packet slot of respective data. The insurance may be lost, for example, when the headset battery is changed, or when the headset is out of range for a duration greater than the TDMA time that the headset can tolerate. This effectively increases the dynamic range of the system. For example, with 30dB of power control, and 70dB of automatic gain control (AGC), the system can acquire insurance over a dynamic range of lOOdB. If a headset detects an incoming call during the data slot of one of the times it listens, it can ring the bell and enter operating mode to allow audio communication. Additionally, if a user activates the handset to make a call, the handset also enters the operating mode, and transmits the appropriate data to the base unit. In the operating mode, when a headset is off hook and is being used, it is deactivated for most of the TDMA time, as in sleep mode, except that it is activated once per time during the two data slots for the headset, and it is also activated for two audio packets (a pair of audio packages) for each field in which a pair of audio slots is assigned. For example, if the 120-L headset is operating, it will be activated by the data slots 251, 252 for each time, and also by the first two audio slots of the even row of each pair of rows (24 audio slots in total). Therefore, in one mode, when in the operating mode, each headset is active only for two data packets and 24 audio packets of the entire TDMA time, a duty cycle of approximately 12 percent (26 slots / ( 9 x 12 x 2 slots)) (assuming that 8 headphones are operating, such that a given handset has two audio slots every third field, instead of each field). In both sleep and operational mode, therefore, the TDMA scheme and the energy saving protocol of the present invention provide energy to be used efficiently, because each operating headset is turned off, and therefore, is not consuming much. energy, for most of the time (whether in sleep or off-hook). This protocol is described in more detail below with reference to Figure 3. Referring now to Figure 3, a state diagram of the energy saving protocol 300 implemented by each handset 120 is shown! of the telephone system 100 of Figure 1, in accordance with one embodiment of the present invention. The protocol 300 comprises four layers: the inactive layer 310, the initialization layer 320, the standby link layer 330, and the active link layer 340. The inactive layer 310 occurs when the handset 120. is out of contact with the base unit 110. The initialization layer 320 occurs when the link is being established, that is, when the handset is in the process of finding the radio frequency channel, the carrier, and the time lags necessary to use the radiofrequency channel, and finally, the TDMA reference for the time. The standby layer 330 is used when the base and the handset have obtained the synchronization lock, and the active link layer 340 exists when there is active audio communication. Accordingly, the waiting layer 330 corresponds to the sleep mode, and the active link layer 340 corresponds to the operating mode. There are three reasons to be in inactive layer 310 (inactive state 311). First, if the handset or base is without power (power failure or battery changes in the handset); second, that the headset is off (de-energized); and third, the handset is out of range. Accordingly, the inactive layer 310 occurs when the handset has been out of synchronization for a prolonged period, such as battery changes, or has been out of range more than local TDMA synchronization can sustain. There are two ways to leave the inactive layer and initiate the initialization state 321 at the initialization layer 320: first, the user can trigger the handset, initiating a search for the synchronization pulses transmitted by the base unit 110 for that handset during its respective data slot; second, the headset periodically starts a search. However, this search is a hungry operation of energy, which requires the continuous operation of the receiver. Accordingly, in a preferred embodiment, the use of energy is limited by reducing the frequency of self-initiated searches to once every several minutes. This allows an inactive headset to recover automatically in the event of a power failure of the base. This technique, therefore, provides a low-cost alternative to the battery backup of the base, and allows automatic recovery if the signal was lost because it was out of range, without excessive draining of the battery. Therefore, in the inactive layer, the handset can be configured to do nothing until the user initiates the establishment of a link, or a periodic timer stimulates the handset to search for transmission of the base synchronization packet. The base transmits contiguous synchronization packets to three different power levels when a link is in the inactive layer, as described above.

Once the handset correlates with a base signal, and leaves the inactive layer 310, the signal must be demodulated, and the handset must verify to determine if it belongs to the base from which it received a signal, and also must exchange. the time stamp information to synchronize the TDMA timers of the base and the handset (states 321, 322 of the initialization layer 320). Once the channel and the TDMA timers are tuned, the link can reach the link link layer 320 (state 331). The time stamps are exchanged between the handset and the base until the time error is below a threshold value, at which point the linked state 331 is achieved. In the standby / sleep mode, while the handset is "linked" ", the handset only periodically checks with the base 110 (i.e., every n seconds or m times) to receive a synchronization packet (data packet having synchronization data), at which point, the TDMA synchronization state is entered. 332, in order to synchronize the local clock. Time stamps are transmitted in the synchronization packet to allow the handset to keep the TDMA time in sync with the base. An "I am alive" recognition pulse can be transmitted back to the base unit 110, when this synchronization packet is successfully received. If the base fails to receive an acknowledgment often enough, the base considers the link broken, and will initiate transmission at multiple power levels, as in the inactive layer. Active communication (operational mode) occurs when the handset initiates a call (state 331 goes to state 342), or when the base requests a handset to answer a call (status 331 goes to state 341). Since the link is operating, they are initiated by exchanging data packets. The data packet indicates that a call is coming in, and the base always monitors the handset transmissions. During active communication, time stamps are not exchanged, but TDMA synchronization is maintained, examining the presence and absence of communication packets. The point where sequential correlation peaks have been observed until they disappear provides a bank that gives a robust indication of the phase of the TDMA chronometer. Because the packets are presented in a consistent manner during active communication, the TDMA phase is maintained by examining the edges of the packets. TDMA frequency insurance is important only for long periods without communication, such as when it occurs in the wait link layer 330 (sleep mode), because the frequency reference is usually provided by a very strong quartz crystal oscillator. precise in both the handset and the base. Upon termination of a call, time stamps will be exchanged at the link-waiting layer 330, to occasionally adjust the local clock, in order to maintain the TDMA reference frequency insurance. The unadjusted TDMA time base is still very accurate, deriving from a quartz oscillator, and will give time out to the TDMA slots over a time with a lot of margin. By adjusting the time base with a guaranteed frequency cycle based on the time stamp, the time base will be accurate over the different TDMA times, allowing the headset to group the data at a minimum speed. An advantage of the protocol of the present invention is that, once synchronized, the handset only needs to group the time slot of the specific data when the timbre and time stamp data would be transmitted. The handset does not even need to group each epoch, since the protocol will allow the user many times to respond to an incoming call, and many times can happen before the base considers that the handset is out of synchronization. Synchronization packets contain timestamps to maintain the frequency of TDMA links secured, and the edges of the data packets maintain the phase of the TDMA links ensured. In the TDMA system of the present invention, which assumes a cluster rate of one second (approximately 20 times of TDMA data) for incoming calls, this is added to an atrial receiver 122 in the duty cycle of approximately 0.02 per second. one hundred (200 microseconds / pack). The recognition would execute the transmitter of the headset 121 at the same speed. One skilled in the art will recognize that the wireless system described above according to the principles of the invention can be a cellular system, wherein the base unit 110 represents a base station serving one of the cells in a cellular telephone network. It will be understood that those skilled in the art can make different changes in the details, materials, and configurations of the parts that have been described and illustrated above, in order to explain the nature of this invention, without departing from the principle and scope of the invention. invention as described in the following claims.

Claims (10)

1. A wireless telephone system (100), in which it comprises: (a) a base unit (110) having a base transceiver (111, 112); and (b) one or more wireless headphones (120), each handset comprising a headset transceiver (121, 122) that establishes a time division multiple access (TDMA) link over a radio frequency channel shared with the base unit ( 110) by means of the base transceiver (111, 112), according to a TDMA time (250) divided into data packet (251, 252) and audio (253, 254) time slots, which are assigned to each headset (120), wherein each headset can be in one of an operational mode and a sleep mode, each headset comprising a local clock and a cascade of counters (210), and a sequence controller timer that remains operational, even when the handset transceiver (121, 122) is deactivated, wherein the local clock and the cascade of meters maintain synchronization between the handset and the base unit, characterized in that, when the handset is in the sleep mode, the handset activate your transceiver ( 121, 122), in response to the timer of the sequence controller, only during its time slot to receive respective data from each Na period, to receive a data packet, and to resynchronize the local clock with the base unit using the data from synchronization contained in the received data packet, wherein the handset can maintain synchronization with the base unit with the local clock and the cascade of counters for a period of time lasting at least N times, without receiving synchronization data from the unit base. The system of claim 1, wherein, after receiving the data packet during the time slot of receiving data from a Na epode, when the handset is in sleep mode, and after resynchronizing the local clock using the synchronization data contained in the received data packet, the handset transmits a data packet to the base unit during the next data transmission time slot, so that the handset notifies the base unit that the handset is still synchronized with the base unit. The system of claim 2, wherein, if the base unit does not receive the data packet from a handset to notify the base unit that the handset is still synchronized with the base unit, after the base unit has transmitted a packet of data to the headset, which contains synchronization information during a Na period, then the base unit tries to re-establish synchronization with the handset, transmitting subsequent data packets to the handset with synchronization information during the time slot of transmitting data for the headset, at increasing power levels. The system of claim 1, wherein, after receiving the data packet during the time slot of receiving data from a N epoch, when the handset is in sleep mode, and after resynchronizing the local clock using the synchronization data contained in the received data packet, the handset transmits a data packet to the base unit during the next time slot to transmit data for the handset, only during each N * k epoch, where k is an integer greater than 1, to notify the base unit that the handset is still synchronized with the base unit. The system of claim 1, wherein N is selected such that the handset can maintain synchronization with the base unit with the local clock and the cascade of counters for a period of time lasting N times, without receiving data. of synchronization from the base unit, and also in such a way that the handset can perform a call monitoring in real time by detecting the data of the incoming call transmitted with a data packet. 6. The system of claim 1, wherein N is a programmable parameter by the user. The system of claim 1, wherein N >; The system of claim 1, wherein the handset is in the operative mode when the handset is off-hook, and is in sleep mode when the handset is on-hook. The system of claim 1, wherein: the epoch has a plurality of pairs of transmission and reception data rows, a pair of rows for each handset; and each headset, when in the operating mode, receives and transmits data packets through the data packet reception and transmission slots, only once during each time, during the pair of transmit and receive data for each headset, and receives and transmits audio packets during the assigned time slot of audio for the handset. The system of claim 1, wherein: each handset is always in a state within one of the following layers: an inactive layer, an initialization layer, a standby link layer, and an active link layer; the inactive layer occurs when the handset is out of contact with the base unit; the initialization layer occurs when a TDMA link is being established between the handset and the base unit; the standby link layer occurs when the base unit and the handset have obtained synchronization insurance, and comprises the sleep mode; and the active link layer occurs when there is active audio communication between the handset and the base unit, and comprises the operating mode.