KR100484593B1 - Wireless telephone system - 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

Wireless telephone system {WIRELESS TELEPHONE SYSTEM}

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.

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 make a phone 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 business with many telephone users. Such a system typically uses a handset that communicates with N handsets simultaneously in a digital communication structure, such as time-division multiple access (TDMA) of spread-spectrum. 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. Conventional power-saving and other TDM type devices for battery powered devices are described in US Pat. No. 4,964,121, filed on September 22, 1992 by Moore, issued October 16, 1990. US Patent No. 5,150,361 to Wieczorek et al. And European Patent Application No. EP 0 726 687 A1 to Nokia Mobile Phones Ltd., published August 14, 1996. Moore's patent describes a TDM system in which a communication channel is divided into a predetermined number of time slots, where the telecommunications unit can communicate with a central control station within the assigned time slot. Moore simultaneously monitors the synchronization signals transmitted intensively within predetermined, allocated time slots for each of the individual radios, but is in a power-saving mode of operation that is virtually current-free outside the radio's pre-allocated time slots. A battery-saving circuit of dedicated individual radios is described. A patent by Wiegjolek, et al., Discloses a TDM operating in a waking energy-saving mode in which a battery-powered communication device shuts down unnecessary circuitry for a predetermined time interval and monitors one of two control slots in a repetitive time frame structure. Describe the system. Nokia's patent describes a wireless telephone system in which the phone can be active during a polling burst and sleep at other times.

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 including a handset transceiver. Each handset establishes a time division multiple access (TDMA) link over a radio frequency channel shared with 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 the synchronous data transmitted in the data packet to synchronize with the base unit, detect incoming call data transmitted in the data packet, or transmit and receive audio information over the TDMA link, if necessary. Power the transceiver of the handset during each data and audio packet time slot of the handset. The handset shuts off the handset's transceiver for the rest of the time to minimize handset power usage.

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 base unit 110 having a receiver unit 112 and a transmitter unit 111, respectively, 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 / receiver unit (transceiver), such as transmitter 121 and receiver 122 of handset 120 ₁ . At any given time, several handsets are operating or are off-hook (ie, making a phone call) (or no handsets are active or off-hook). Thus, system 100 provides a wireless network between base unit 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, system 100 employs a digital TDMA structure, as described in more detail below, which allows for efficient use of power, as each operating handset is " Off "state (i.e., not transmitting or receiving data, and thus not consuming much battery power) and being only" on "during a unique time slice or slot, as described in more detail below. to be. In one embodiment, the handset shuts off power by at least powering off its CPU and transceiver (receiver and transmitter) units, with the clock and associated timer or Maintain power only for the supervisory circuit.

However, using time-division multiplexing (TDM) techniques such as TDMA and turning on each transceiver only during unique time slots can cause various problems. For example, since the handset uses a radio frequency 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, thereby activating the other handset. May cause unnecessary battery drain. Thus, the handsets in the present invention are carefully synchronized so that each handset only "listens" for transmission messages in its own time slot.

Without the present invention, the local time base of the handset could be flexible over time, which would eventually cause each handset to receive all outgoing messages to resynchronize to the base unit 110 after a period of time. After this synchronization, the handset will once again be able to receive only within its own 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 allow this power to be turned 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 receive only in the appropriate time slots in synchronization with a particular 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 that are 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), the handset of the eight {e.g., a handset (120 ₁ - 120 ₈ )} is shown assuming that it can be activated or operated simultaneously. The structure 250 of a TDMA interval includes a number of rows and columns. Each row of TDMA structure 250 represents a digital data field of 2 ms and is grouped odd or even in pairs of odd or even respective rows or fields. The TDMA interval structure 250 has a 48 ms interval.

Each field of digital data includes a total of nine packets (data packets 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 audio transmission of the base unit {from base unit 110 to a given handset} and audio transmission of the handset (given handset to base unit). It contains one packet. Each data packet is a collection of data transmitted from a base unit to a given handset or vice versa during discontinuous time slots where no other handset receives or transmits data over the system's data channel. These data packets may be of 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 also 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. Is a set of.

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 the twelve 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 that the handset 120 ₁ is in operation (off hook state) and the audio packet is transmitted to the handset 120 ₁ in the audio packet slot 253, the audio packet Is transmitted by the handset 120 ₁ to the base unit 110 in the audio packet slot 254, and so on for the other three handsets until the field or row ends. In an odd row of pairs of rows (0), data slot 252 is used to receive data sent from handset 120 ₁ to base unit 110, and audio packets are sent to the remaining eight active handsets. In the row pairs 1-11, the same sequence occurs except that the data packets are sent to and from a different handset than the row pair 0.

In the present invention, a time base capable of analyzing a fraction of time slots over a period of several seconds is established in each handset that matches the TDMA slot timing in base unit 110. TDMA interval structure 250 is known to each handset and base unit, and once the time base is synchronized, the handset receiver will know when it can receive transmission messages from the base and when You will also know if you need to resend the data. In order to maintain a known TDMA slot in microseconds over a one second interval, it is necessary to provide a very stable and accurate reference for operating 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 proceed step by step). The reference clock signal is provided by the local clock of the handset, which local clock is periodically adjusted as needed for correction of 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 columns in the current field or row of the TDMA interval structure 250). 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 transmitted 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 the sleep mode, the handset is configured to wake up for the assigned " receive data " slot and then " listen " the data and then turn off again if there is no incoming call. This waking operation is generated by a watchdog timer that counts down to a specific value and turns on the CPU and other components needed to receive and / or transmit data. 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 is informed that the handset is active and synchronized by sending the appropriate data message (“I'm alive”) to the base unit 110. Can 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 power is turned on to allow the handset to receive data packet transmissions from the base unit 110, the handset remains synchronized (i.e., keeps the communication loop locked) and the incoming call is It is sufficient once in a 48ms interval to be detected fast enough to alert the user of an incoming call (to see 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 wakes up during the data slots of the handset, for example only once every third interval, which also monitors synchronization and real-time incoming calls. It will be enough. This further reduces the duty cycle. A “I'm alive” message sent from the handset (eg, sent in data slot 252) may be sent every interval or even when the handset is awake to receive data from base unit 110. It does not have to be transmitted for each interval. Preferably, these parameters are user programmable. For example, the handset may be programmed to wake up every third interval, receive during its own data slot, 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 every sixth interval, the handset is sufficient. 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 may be lost when the handset's battery is replaced, or when the handset is out of service for a longer time period than the inherent 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 that the handset is receiving, the handset makes a phone call and enters an active 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 is turned 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) The handset is inactive during most TDMA periods, as in sleep mode, except when turned on. 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 the RF channel, the carrier and the timing offset required to use the RF channel, and finally the 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). First, if there is no power to the handset or base (handset power off or battery replacement), second, when the handset is off (no power), and third, the handset is out of service range. 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-initiated searches to once every few minutes. This allows the inactive handset to recover automatically in the event of a base power cut. Thus, this technique provides a low cost alternative to base battery backup, and this technique allows for automatic recovery without excessive battery drain if the signal is lost 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 prompts the handset to search for transmission 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 exits 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. Time stamp information must also be exchanged (states 321 and 322 of initialization layer 320) in order to synchronize them. 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 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, to receive a synchronization packet (a data packet with synchronization data). The base 110 is only checked periodically (ie every n seconds or m interval). The time stamp is sent included in the synchronization packet to keep the handset in sync with the TDMA time. 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 the base requests a response to the call of the handset (state 331 to state 341). ) Occurs. Since the link is operational, the handset is initiated by exchanging data packets. The data packet indicates that the call has arrived 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, time stamps will be exchanged at standby link layer 330 to adjust the local clock from time to time 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 adjusting the time base to 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 particular 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 incoming calls 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 acknowledgment will operate the handset transmitter 121 at this same rate. The practitioner will appreciate that, according to the principles of the present invention, the wireless system described above represents a base station in which the base unit 110 is responsible for one cell in a cellular telephone network. It will be appreciated that it may be a cellular system. 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.

As mentioned above, the present invention is applicable to a technique for saving power in a battery-operated wireless handset of a multi-line wireless telephone system, especially a wireless telephone system.

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Claims (12)

(a) a base unit (110) having base transceivers (111, 112); (b) one or more wireless handsets 120, each handset having time-division multiple access (TDMA) divided into data 251, 252 and audio 253, 254 packet time slots assigned to each handset 120; : Handset for establishing a TDMA link via a radio frequency (RF) channel shared with the base unit 110 via the base transceivers 111 and 112, according to a time division multiple access) epoch 250. One or more wireless handsets 120, including transceivers 121 and 122, As a wireless telephone system 100, including, Each handset may be in one of an operation mode and a sleep mode, and each handset may include a watchdog timer and a serial connection that maintain an operation state even when the power of the handset transceivers 121 and 122 is cut off. Includes a counter 210 and a local clock, The local clock and serial connection counter maintain synchronization between the handset and the base unit; In the wireless telephone system 100, When the handset is in sleep mode, the handset receives the data packet and uses the synchronization data included in the received data packet to resynchronize the local clock with the base unit, the handset in every Nth interval. Only during each received data time slot of powers the transceivers 121, 122 of the handset in response to a watchdog timer, The handset can maintain synchronization with the base unit via the local clock and a serial connection counter over a time period over at least N intervals without receiving synchronization data from the base unit. , Wireless phone system. 2. The local clock of claim 1, wherein after receiving the data packet during the received data time slot of the N-th interval when the handset is in sleep mode, the local clock is reset using the synchronization data included in the received data packet. After synchronizing, the handset sends a data packet to the base unit during the next transmission data time slot for the handset to inform the base unit that the handset is still in sync with the base unit. . 3. The handset of claim 2, wherein after the base unit transmits a data packet containing synchronization information to the handset during the Nth interval, the handset notifying the base unit if the handset is still synchronized with the base unit. If the base unit fails to receive the data packet from the base unit, during the transmission data time slot for the handset, the base unit transmits a sequential data packet with synchronization information at an increased power level to the handset, Attempting to regain the state of synchronization, wireless telephone system. 2. The method of claim 1, wherein after receiving the data packet during the received data time slot of the Nth interval when the handset is in sleep mode, and using the synchronization data included in the received data packet to clock the local clock. After resynchronization, the handset transmits a data packet to the base unit during the next transmit data time slot for the handset only during every N * kth interval, where k is an integer greater than 1, so that the handset still And notifying the base unit that it is synchronized with the base unit. The method of claim 1, wherein the handset is capable of maintaining synchronization with the base unit via the local clock and serial connection counter over a period of time over N intervals without receiving synchronization data from the base unit, And N is selected so that the handset can perform real-time call monitoring by detecting incoming call data sent with the data packet. The system of claim 1 wherein N is a user programmable parameter. The radiotelephone system of claim 1 wherein N> 1. 10. The system of claim 1 wherein the handset is in the operational mode when off hook and in the sleep mode when on hook. 2. The apparatus of claim 1, wherein the interval has a plurality of row and transmit data row pairs, each for each of the handsets, Each handset receives and transmits a data packet through a receive and transmit data packet slot only once during each interval during the pair of transmit and receive data rows for each of the operating handsets, when in the operating mode. And receive and transmit an audio packet during an assigned audio time slot of the interval for. The method of claim 1, wherein each handset is always in a state within 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 being 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. delete delete