KR20010032993A - Power saving protocol for tdma multi-line wireless telephone handsets - Google Patents

Abstract

The wireless telephone system includes a base unit having a base transceiver and a plurality of wireless handsets, each handset having a handset transceiver. Each handset establishes a time-division multiple access (TDMA) link through a radio frequency (RF) channel shared with the base unit through the base transceiver according to a TDMA epoch, and the base unit Assigns a unique data and audio packet time slot to each handset. Each handset uses the synchronization data sent with the data packet to synchronize with the base unit, and as needed to detect incoming call data sent with the data packet or to transmit and receive audio information over the TDMA link. Power the transceivers of each handset during each data and audio packet time slot of the handset. The handset powers off the transceiver of the handset during this period other than the data and audio packet time slots to minimize handset power usage.

Description

POWER SAVING PROTOCOL FOR TDMA MULTI-LINE WIRELESS TELEPHONE HANDSETS}

Telephones and telephone systems, including wireless telephone systems, are widely used. In a cordless telephone system, a cordless or cordless telephone handset unit communicates with a base unit via analog or digital radio signals, which are typically connected to an external telephone network through a standard telephone line. . In this manner, a user can use this wireless handset to initiate a telephone call with another user through the base unit and the telephone network.

Multi-line wireless telephone systems are also used in a variety of situations, such as transactions with many telephone users. Such systems typically use handsets that simultaneously communicate with up to N handsets in a digital communication structure such as spread-spectrum time division multiple access (TDMA). In a TDMA system, a single radio frequency (RF) channel is used, with each handset transmitting and receiving data during a dedicated time slice or slot within an entire cycle or epoch. Since handsets typically use battery power, the use of efficient power in wireless systems is important.

TECHNICAL FIELD The present invention relates to a multi-line wireless telephone system, and more particularly to a technique for saving power in a battery operated wireless handset of a wireless telephone system.

1 is a block diagram of a TDMA multi-line wireless telephone system in accordance with an embodiment of the present invention.

FIG. 2 is a schematic diagram of a TDMA slot structure and handset counter used in the TDMA configuration of the system of FIG. 1 in accordance with an embodiment of the present invention. FIG.

3 is a state diagram of a power saving protocol implemented by each handset of the telephone system of FIG. 1 in accordance with an embodiment of the present invention.

The wireless telephone system includes a base unit having a base transceiver and one or more wireless handsets each comprising a handset transceiver. Each handset establishes a time division multiple access (TDMA) link over a radio frequency channel shared to the base unit via a base transceiver according to the TDMA interval, where the base unit assigns a unique data and audio packet time slot to each handset. . Each handset uses each piece of the handset required to synchronize with the base unit using the synchronous data sent in the data packet, to detect incoming call data sent in the data packet, or to transmit and receive audio information over the TDMA link. Powers the handset's transceiver during the data and audio packet time slots. The handset shuts down the handset's transceiver for the rest of the time to minimize power consumption.

1, a block diagram of a TDMA multi-line wireless telephone system 100 is shown, in accordance with an embodiment of the present invention. The TDMA system 100 includes a receiver unit 112 and a transmitter unit 111, respectively, and includes a base unit 110 connected to an external telephone network 116 via telephone line (s) 115. System 100 also includes N wireless handsets 120 ₁ , 120 ₂ ,... 120 _N. Each has a transmitter and receiver unit (transceiver), such as transmitter 121 and receiver 122 of handset 120 ₁ . At any given time, several (or none) handsets are operating or off-hook (ie, making a phone call). Thus, system 100 provides a wireless network between base station 110 and each handset 120 _i (1 ≦ _i ≦ N). In one embodiment, the system 100 includes four handsets (120 ₁ -120 ₄₎ that may be all active at the same time. In another embodiment, the system 100 includes a varying number of handsets, for example up to eight of which may be activated or operated at the time N = 12.

As described above, handsets generally use battery power, so efficient power utilization is important for wireless telephone systems. Thus, in one embodiment, the present invention includes a TDMA system and protocol for connecting multiple transceivers to a base unit over a single radio frequency channel. In particular, the system 100 uses a digital TDMA structure as described in more detail below, which allows for efficient use of power, in which each operating handset is " off 'for most of the area of the TDMA interval. "State" (i.e., not transmitting or receiving data, and thus not consuming much battery power) and "only" during the time slice or slot of the handset itself, as described in more detail below. . In one embodiment, the handset shuts off power by at least powering off its CPU and transceiver (receiver and transmitter) units, with a clock and associated timers or the like sufficient to wake up the CPU in a predetermined time slot. Maintain power only for the supervisory circuit.

However, the use of a time-division multiplexing (TDM) technique such as TDMA and turning on each transceiver only during the transceiver's own time slot can cause various problems. For example, because the handset uses a wireless energy detector to detect when a signal is transmitted from the base unit 110 to one of the handsets, communication to one handset activates the other handset, thus enabling May cause unnecessary battery drain. Thus, the handsets in the present invention are carefully synchronized so that each handset only "listens" the transmission message in its own time slot.

Without the present invention, the local time base of the handset could flow over time, which would eventually cause each handset to listen to all outgoing messages to resynchronize the base unit 110 after a period of time. After this synchronization, the handset will once again hear only its time slot. However, since "listening" requires power, the power of the battery will be wasted when synchronization is compromised. In addition, if synchronization is compromised, link integrity may be compromised due to signal collisions, which occur when multiple devices attempt to use a single radio frequency channel at the same time.

Thus, each handset 121 _i uses the protocol of the present invention to turn this power on and off without compromising synchronization, as described further below. The synchronization protocol of the present invention allows each remote independent handset to synchronize to the TDMA sequence from the base unit using a local time base, and to listen to only the appropriate time slots in synchronization with a specific transmission from the base unit.

Referring now to FIG. 2, in accordance with one embodiment of the present invention, a TDMA slot structure 250 and a handset counter 210 used in the TDMA configuration 200 for the system of FIG. 1 are schematically illustrated. System 100 uses a TDMA epoch having structure 250, the structure 250 has a total of twelve handsets (120 ₁ -120 _12), double-eight handsets {e.g., a handset (120 ₁ -120 ₈ )} is shown assuming that it can be activated or operated simultaneously. TDMA interval structure 250 includes many rows and columns. Each row of the TDMA structure 250 represents a digital data field of 2 ms and is even or odd, grouped in odd or even pairs for each row or field, respectively. The TDMA interval structure 250 has a 48 ms interval.

Each field of digital data includes a total of nine packets (eight packets of data in the first column (data packets transmitted from the base unit or handset) and eight audio packets grouped into four pairs of two). Each pair of audio packets in a row contains one packet (time slot) for base audio transmission (from base unit 110 to a given handset) and one handset audio transmission (from a given handset to base unit). Contains a packet. Each data packet is a collection of data transmitted from a base unit to a given handset or vice versa during discrete time slots where no other handset receives or transmits data over the system's data channel. These data packets may contain various types of data, such as synchronization data or words with time stamp information, caller ID information, incoming caller information, and similar information sent to the handset in sleep mode. It may include. The data packet sent from the handset to the base unit may contain information such as a telephone number dialed by this handset. Each audio packet is again a portion of the audio data transmitted from the base unit to the given handset or vice versa during a given time slot of the entire period, during which time no other handset receives or transmits data over the system's single radio frequency channel. It is a set.

Thus, for example, a row pair (0) includes even rows and odd rows. In an even row, the base unit transmits data to one of 12 handsets, such as handset 120 ₁ , in a first time slot (slot 251). There is one row pair in section 250 for each handset so that each handset can transmit and receive data to base unit 110 once per section. After the first data slot 251, assuming the handset 120 ₁ is in operation {off hook state} and the audio packet is transmitted from the audio packet slot 253 to the handset 120 ₁ , audio The packet is transmitted by the handset 120 ₁ from the audio packet slot 254 to the base unit 110, and the same is done for the other three handsets until the field or row ends. In the odd row of the pair of rows (0), the data slot 252 is used to receive data transmitted from the handset 120 ₁ to the base unit 110, and an audio packet is transmitted for the remaining eight active handsets. . In the row pairs 1-11, the data packets occur in the same sequence except that they are sent to and from a different handset than the row pair 0.

In the present invention, a time base capable of breaking up a fraction of time slots over a period of every second is established in each handset that matches the TDMA slot timing in base unit 110. TDMA interval structure 250 is known by both the handset and the base unit, and once the time base is synchronized, the handset receiver will know when to hear the transmission message from the base and when the data at the base. You will also know if you need to resend. To maintain a known TDMA slot in microseconds over a one second interval, a very stable and accurate criterion must be provided to operate this time base.

To eliminate collisions in the protocol, every handset is given a fixed data time slot, and as the handset needs an audio time slot, this audio time slot is dynamically allocated. This information is communicated over a data channel (first column of TDMA structure 250). The TDMA slot is divided into data and audio slots in a two dimensional array as shown in FIG. The base sends a synchronization packet to the handset in each data slot until the call is initiated.

Each handset keeps the serial connection 210 of the counters in sync with the TDMA sequence by preventing variations in the local timing of each handset. This is done by applying a reference clock signal to the first counter 211 (all counters are initialized at some earlier point in time so that initialization can be performed step by step). The reference clock signal is provided by the local clock of the handset, which local clock is periodically adjusted as needed to correct for variations, in accordance with the time stamp synchronization information transmitted during the data packet slot by the base unit 110. Counter 211 continues to track sub-packet decomposition and identifies how many bits of the packet are processed (e.g., how many bits out of 100 bits per audio packet). The counter 212 keeps track of horizontal packets or time slots (ie, the number of fields in the TDMA interval structure 250 or columns of the current row). The counter 213 keeps track of whether the current row is odd or even, and the counter 214 determines whether the current packet is a data packet and which handset the data packet is correlated with and whether this data packet is associated with the base unit 110. Keep track of whether it is transmitted from the < RTI ID = 0.0 > Finally, the counter 215 keeps track of which section the system 100 is in. This may be useful, for example, to require retransmission of corrupted data sent by the base unit 110 during a particular interval.

The TDMA system of the present invention saves power by turning off most components of the handset except for the internal clock and supervisory circuits for most of the TDMA period. Internal clocks and protocols implemented by each handset ensure that synchronization is not compromised, even if the power of the handset is lowered. Thus, power is saved, but synchronization is not compromised. Each handset is in one of two states: sleep mode or active mode.

In sleep mode, when the handset is on hook, only the internal clock and watchdog timer continue to run, with the clock already synchronized to the base unit clock and interval. Thus, in sleep mode, the handset is configured to stay awake for an assigned " receive data " slot and " hear " data, then turn off again if no incoming call exists. This waking operation is generated by a watchdog timer and / or transmission data that counts down certain values and turns on the CPU and other components needed to listen. During this data slot, the handset receives the synchronization data from the base unit 110 and adjusts its internal clock to correct for any variation if necessary. In the next data slot, the handset indicates that the handset is active and synchronized by sending the appropriate data message (“I'm alive”) to the base unit 110. To stay awake again. Thus, in one embodiment, when in sleep mode, each handset has only two data packets of the entire TDMA interval, that is, for a duty cycle of approximately 0.93% {2 slots / (9 × 12 × 2 slots)}. Lights up. When the handset is powered up to hear the data packet transmission from the base unit 110, the handset remains synchronized (i.e., keeps the communication loop locked) and also the incoming call. It is sufficient once every 48ms to allow any incoming call to be detected fast enough to alert the user of this incoming call (to view caller ID information and / or to make the call answered in real time). .

In an alternative embodiment, the handset skips multiple sections as a whole and is awake during the data slots of the handset, for example only once every third interval, which also monitors synchronization and real-time incoming calls. Will be enough. This further reduces the duty cycle. The “I'm alive” message sent from the handset (eg, sent in data slot 252) is sent every interval, or even every time the handset is awake to hear data from base unit 110. It does not have to be sent every time. Preferably, these parameters are user programmable. For example, the handset is awake every third interval and can be programmed to listen for its own data slots and send an "I'm alive" message back to the base unit every sixth interval. In this case, a base unit that does not have similar power constraints can transmit synchronization data every interval, but as long as the "I'm alive" data message is received for every sixth interval, the handset is sufficiently large. You will notice that it is synchronized. If an "I'm alive" data message is not received, the base unit 110 may assume that the lock has been lost, where the base unit 110 may, for example, during each data packet slot of the handset. You may want to recover the link by sending data / synchronization packets to the compromised handset at three higher power levels. For example, locks can be lost when the handset's battery is replaced, or when the handset is out of service for longer than its TDMA timing allows. This effectively increases the dynamic range of the system. For example, with 30 dB of power control and 70 dB of automatic gain control (AGC), the system can acquire locks over a 100 dB dynamic range.

If the handset detects an incoming call during a data slot in one of the sections the handset is listening to, the handset dials into operational mode to enable audio communication. In addition, if the user turns on the handset to make a call, the handset also enters the operating mode and sends the appropriate data to the base unit.

In the operating mode, when the handset is off hook and in use, the handset turns on once for each interval between two data slots for the handset, and also two audio packets (audio packets in every field to which an audio slot pair is allocated). Except for turning it on, the handset is inactive for most TDMA periods, such as in sleep mode. For example, if the handset 120 ₁ is in operation, the handset will display the first two audio slots (24 audio totals) for the data slots 251 and 252 during each interval and also for the even row in each row pair. Slot). Thus, in one embodiment, when in operational mode, each handset has 24 audio packets and only two data packets of the entire TDMA interval, a duty cycle of approximately 12% {(26 slots / (9 × 12 × 2 slots)}). (Assuming eight handsets are operating, so that a given handset has two audio slots in another field across one field rather than every field).

Thus, in sleep mode and in operation mode, the TDMA architecture and power saving protocol of the present invention powers each handset off most of the time (whether in sleep mode or off hook state), and therefore does not consume much power. To be used effectively. This protocol is described in more detail below with reference to FIG. 3.

Referring now to FIG. 3, shown is a state diagram of a power saving protocol 300 implemented by each handset 120 _i of the telephone system 100 of FIG. 1, in accordance with an embodiment of the present invention. Protocol 300 includes four layers (inactive layer 310, initiation layer 320, standby link layer 330 and active link layer 340). Inactive layer 310 occurs when handset 120 _i is not connected to base unit 110. When the link is established, i.e., the handset is in the process of finding an RF channel, a carrier and a timing offset required to use the RF channel, and finally a TDMA reference during the interval, the initialization layer 320 occurs. The standby layer 330 is used when the base and handset are in a synchronized lock state, and the active link layer 340 occurs when active audio communication. Accordingly, the standby layer 330 corresponds to a sleep mode, and the active link layer 340 corresponds to an operation mode.

There are three reasons for being in the inactive layer 310 (inactive state 311). The first is if there is no power to the handset or base (handset is low or the battery is replaced), the second is when the handset is off (no power), and the third is when the handset is out of service. It is when there is. Thus, the inactive layer 310 occurs when the handset is asynchronous for extended periods, such as battery replacement, or out of service for longer than local TDMA synchronization can maintain. There are two ways to enter the initialization state 321 of the initialization layer 320, leaving the inactive layer. The first is that the user triggers the handset to initiate a search for synchronization pulses sent by the base unit 110 for the handset during each data slot of the handset, and the second handset periodically initiates a search. It's self-initiating. However, this search is an operation that requires a lot of power, requiring continuous operation of the receiver.

Thus, in a preferred embodiment, the use of power is limited by reducing the frequency of self-initialized searches to once every few minutes. This allows the inactive handset to recover automatically in case of low base power. Thus, this technique provides a low cost alternative to base battery backup, and this technique allows automatic recovery without excessive battery drain if the signal is damaged because it is out of service range. Thus, in the inactive layer, the handset may be configured to do nothing until the user initiates the establishment of the link or until the periodic timer stimulates the handset to search for a transmission tone of the base synchronization packet. As previously described, when the link is in the inactive layer, the base continues to transmit synchronization packets at three different power levels.

If the handset correlates with the base unit signal and leaves the inactive layer 310, the signal must be demodulated, the handset must check to determine if the received signal belongs to the base, and the handset has a base and handset TDMA timer. The time stamp information must also be exchanged (state 321, 322 of the initialization layer 320) in order to synchronize. Once the channel and the TDMA timer are tuned, the link can reach the idle link layer 330 (state 331). The time stamp is exchanged between the handset and the base until there is a timing error below the threshold at which the linked state 331 is achieved.

In the standby / sleep mode, while the handset is in the " linked " state, at the time the handset enters the TDMA synchronization state 332 to synchronize the local clock, receiving a synchronization packet (data packet with synchronization data). In order to check the base 110 only periodically (ie every n seconds or m interval). The time stamp is sent in a synchronization packet to allow the handset to keep TDMA time synchronized with the base. An “I'm alive” acknowledgment pulse may be sent back to the base unit 110 when this synchronization packet is successfully received. If the base fails to receive an acknowledgment pulse often enough, the base will consider the link broken and will begin transmitting at multiple power levels as in the inactive layer.

Active communication (operation mode) when the handset initiates a call (moves from state 331 to state 342) or when the base requests a response to the call of the handset (moves state 331 to state 341). ) Occurs. As the link operates, the handset is initialized by exchanging data packets. The data packet indicates that the call is received and the base always monitors the handset transmission. During active communication, time stamps are not exchanged, but TDMA synchronization is maintained by checking for the presence or absence of communication packets. The point where sequential correlation peaks have been observed until disappearing provides an edge that gives a robust indication of the phase of the TDMA timer. Since packets occur consistently during active communication, the TDMA phase is maintained by checking the edges of the packets.

TDMA frequency lock is important only if there is no communication for a long time, such as occurs in standby link layer 330 (sleep mode), because the frequency reference is typically provided by a very accurate crystal oscillator on both the handset and base. . Upon completion of the call, the time stamps will be exchanged at the standby link layer 330 from time to time to adjust the local clock to maintain the TDMA reference frequency lock. The unadjusted TDMA time base is still quite accurate because it is derived from the crystal oscillator and will not time out with the TDMA slots by much difference during one interval. By coordinating the time base with the frequency locked loop based on the time stamp, the time base will be accurate over several TDMA intervals, which allows the handset to poll data at least at a rate.

One advantage of the protocol of the present invention is that once synchronized, the handset only needs to poll a specific data time slot to which the ring and time stamp data will be transmitted. The handset does not even need to poll every interval since the protocol will allow the user to answer the incoming call in many intervals, many of which will pass before the base considers the handset asynchronous. The synchronization packet includes a time stamp to keep the TDMA link in frequency locked state, and the edge of the data packet causes the TDMA link phase to remain locked. In the TDMA system of the present invention, assuming that the polling rate for an incoming call is 1 second for a 20 TDMA data interval, this corresponds to the handset receiver 122 for a duty cycle of approximately 0.02% (200 ms / packet). . The grant will operate the handset transmitter 121 at this same rate.

Those skilled in the art will appreciate that the wireless system described above in accordance with the principles of the present invention may be a cellular system in which base unit 110 represents a base station operating as a cell in a cellular telephone network.

Various modifications in the details, materials, and arrangements of the elements described above to illustrate the characteristics of the present invention, and that the changes can be made by those skilled in the art without departing from the spirit and scope of the invention mentioned in the appended claims. I can understand.

Claims (12)

In a wireless telephone system, (a) a base unit having a base transceiver, and (b) one or more wireless handsets, each handset via the base transceiver for allocating packet time slots to each handset according to a time-division multiple access (TDMA) epoch; A plurality of wireless handsets, comprising a handset transceiver for establishing a TDMA link over a radio frequency (RF) channel shared with the base unit, Each handset is adapted to power a transceiver of each handset during a packet time slot of each handset for synchronization with the base unit, each handset being transceiver of each handset during the interval other than a packet time slot. A wireless telephone system, which is adapted to cut off power. 10. The apparatus of claim 1, wherein each handset is configured to detect incoming call data sent with a data packet or to transmit and receive audio information over the TDMA link during each data and audio packet time slot of the handset. And further adapted to power a transceiver of the handset. 2. The apparatus of claim 1, wherein the epoch has a plurality of row and transmit data row pairs, given one row pair for each handset, Each handset receives and transmits a data packet through a receive and transmit data packet slot during the pair of transmit and receive data rows for each of the operating handsets only once during each interval when in the operating mode, each handset And receive and transmit an audio packet during the assigned audio time slot of the interval for. The method of claim 1, wherein each handset may be in an operational mode when the handset is off hook or in a sleep mode when the handset is on hook. Wherein each handset includes a local clock and watchdog timer that maintain operation even when the handset transceiver is powered off, When the handset is in the sleep mode, it is necessary to synchronize with the base unit by synchronizing with the synchronization information included in the received data packet, so that the handset receives the received data packet time of each of the handsets during the interval. And power the transceiver of the handset in response to the watchdog timer during a slot. 5. The apparatus of claim 4, wherein each handset is always in a state of one of an inactive layer, an initiation layer, a standby link layer, and an active link layer. The inactive layer occurs when the handset is not connected with the base unit, The initialization layer occurs when a TDMA link is established between the handset and the base unit, The standby link layer occurs when the base unit and the handset have acquired a synchronization lock, and include the sleep mode, The active link layer occurs when there is active audio communication between the handset and the base unit and includes the operating mode. 5. The apparatus of claim 4, wherein when the handset is in sleep mode, the handset supplies power to the handset transceiver during each of the received data time slots of the handset during each interval to receive a data packet including synchronization information. , Wireless phone system. 7. The transmission data time slot of claim 6, wherein during the received data time slot, after receiving the data packet, to notify the base unit that the handset is still synchronized with the base unit. While the handset transmits a data packet to the base unit. 8. The method of claim 7, wherein after the base unit transmits a data packet containing synchronization information to the handset, the base unit notifies the base unit that the handset is still in sync with the base unit. A note, if not receiving the data packet from the handset, during the transmission data time slot for the handset, the base unit transmits a sequential data packet with synchronization information at the increased power level to the handset, thereby communicating with the handset. A wireless telephone system that attempts to regain synchronization. 5. The apparatus of claim 4, wherein when the handset is in sleep mode, the handset supplies power to the transceiver of the handset during each received data time slot of the handset in every Nth interval, wherein the handset receives data from the base unit. A wireless telephone system capable of maintaining synchronization with the base unit over a time period lasting at least N sections without receiving a packet. The apparatus of claim 4, wherein when the handset is in a sleep mode, the handset is required to synchronize with the base unit by synchronizing with the synchronization information included in the received data packet. And power the transceiver of the handset in response to the watchdog timer during a received data packet time slot. A wireless telephone communication method of a wireless telephone system in which a base unit having a base transceiver and at least one wireless handset each handset having a handset transceiver are provided. (a) a radio frequency channel shared between the base unit and the handset, having the handset transceiver for each handset and assigning unique data and audio packet time slots to each handset according to a TDMA interval through the base transceiver; Establishing a time division multiple access (TDMA) link via (b) for each handset, power on the transceiver of each handset during each data and audio packet time slot of each handset as needed to synchronize with the base unit using the synchronization data transmitted with the data packet. Supplying, and (c) for each handset, powering off the handset transceiver during the interval other than the data and audio packet time slots to minimize handset power usage. In the wireless handset for use in a wireless telephone system having a base unit having a plurality of wireless handsets and a base transceiver, each wireless handset having a handset transceiver, (a) establish a time division multiple access (TDMA) link over a radio frequency channel shared with the base unit which assigns unique data and audio packet time slots to each of the plurality of handsets according to a TDMA interval through the base transceiver; Handset transceiver, (b) means for powering the transceiver of each handset during each data and audio packet time slot of each handset, as necessary to synchronize with the base unit using the synchronization data transmitted with the data packet; And (c) means for disconnecting power to the handset transceiver during the interval other than the data and audio packet time slots to minimize handset power usage.