Method and system for providing access to a channel for voice transmissions

The present invention relates to a wireless communication system. More specifically, the present invention relates to voice transmission in a time division multiple access (TDMA) system.

In general, a wireless communication system may include a set of "subscriber devices", a set of "base radios", and a relay means. Typically, the subscriber device is the end point of the communication path and the "base radio" is fixed. Also, the relay means establishes or maintains a communication path to the subscriber device (SU). One such type of system is a time division multiple access (TDMA) communication system. In the TDMA communication system, the wireless medium is divided into time slots in order to carry the communication of the system. Since the wireless medium is a shared medium, it is necessary to control access to the wireless medium and enable the SU to use the wireless medium for voice communication.

Specifically, in order for a SU to carry out transmission, it must first activate the base radio (BR) and obtain synchronization. Upon obtaining the synchronization, the SU requests that the call be set up and sends it over the radio medium. Since BR needs to be activated and synchronized, the call requires extra time. Therefore, it is desirable to avoid these procedures and reduce the amount of time required to make a call. In addition, certain SUs may require preferential access to the radio medium and may need to be given access to the radio medium for transmission during active call conditions.

Therefore, there is a need to provide access to voice communication channels.

See Figure 1 here. FIG. 1 shows an example of a method and apparatus of the present invention that can be adopted and incorporated in a typical wireless communication system 100. The example shown consists of a plurality of cells, each equipped with a base radio (BR) 3,5,7,9,11,13 and a plurality of subscriber devices 12,14,16,18,20,22. Typically, the base radio is located in the center of the cell. The subscriber devices 12,14,16,18,20,22 transmit and receive communication with the base radios 3,5,7,9,11,13.

Preferably, the subscriber device (SU) is mobile capable of communicating with BR using time division multiple access (TDMA) or time division duplex (TDD) technology, as further described herein. Includes devices or mobile devices (such as in-vehicle or portable radio or radiotelephones). In TDMA or TDD technology, a specified time segment is divided into time slots assigned for individual communications. In one typical embodiment of the invention, the wireless communication system 100 is assumed to be a two-slot TDMA communication system, however, the spirit and scope of the invention also when other slot ratios are used in the TDMA communication system. Is in. In one typical embodiment, voice communication is initiated by pressing PTT (Push to Talk), and the SU sends a wireless media request to BR.

Preferably, the BR is equipped with fixed equipment for communicating data / control and voice information between SUs in order to carry out communication between SUs in the wireless communication system 100. An exemplary embodiment of the invention includes a dekey BR after 5 seconds of determining that there is no valid SU activity on the radio medium. In one typical embodiment, such a timer is referred to as a subscriber inactivity timer (SIT). In such an embodiment, the SIT unlocks after 5 seconds of determining that there is no valid SU activity on either of the two time slots of the TDMA communication system. The SIT is started when there is no valid SU activity on the radio medium, and stopped when the BR determines that there is a valid SU activity on the radio medium. In yet another exemplary embodiment, the wireless communication system 100 comprises a BR that unlocks after 180 seconds. Such a period is supplied to BR and is called a timeout timer (TOT). The TOT is reset when a new SU transmission is detected on the radio medium. The TOT is stopped when the BR unlocks due to a SIT timeout, and the BR unlocks when the ending TOT in any ongoing communication expires.

The communication initiated or repeated by the BR and transmitted to the subscriber device (SU) is called the downlink, and the communication initiated by the SU and transmitted to the BR is called the uplink. In one typical embodiment, each BR3,5,7,9,11,13 does not continuously transmit downlink communication, but the time slot transmitted between BR and SU becomes the BR downlink. Each BR maintains a synchronized communication so that it is synchronized based on.

In one embodiment of the example, synchronization is provided by a message that identifies the center of the TDMA burst. In SU or BR, the receiver uses matched filters and correlators to perform symbol recovery to identify the center of the TDMA burst. When the receiver is synchronized with the channel, the receiver uses pattern matching to detect the presence of a message that identifies whether the channel is present and synchronized. This message identifies the type of synchronization that exists on the channel. In one exemplary embodiment, the message is a) to distinguish voice bursts from data / control bursts and reverse channel bursts, b) to distinguish between inbound and outbound channels, and c) a channel modulation format, For example, it is used to distinguish between Motorola P25 Phase 1 FDMA and Motorola P25 Phase 2 TDMA, and d) the type of wireless communication system, eg, the Motorola P25 system and the Motorola low-rise digital system.

As used herein, the terms "communication" and "transmission" are used interchangeably to represent consecutive TDMA bursts emanating from one radio in one time slot. Therefore, transmission can collectively represent voice, data or control information associated with the wireless communication system 100. The term "call" refers to the associated voice transmission between SUs in wireless communication system 100. In one typical embodiment, the voice transmission in the call is separated by idle time. The idle time is signaled by a message notifying the subscriber that the radio medium is idle. In addition, since idle time occurs on the uplink, the message notifying the subscriber that the radio medium is idle is transmitted on the downlink.

As is known in the art, the term "burst" refers to the smallest independent unit of TDMA transmission. In one exemplary embodiment, in bursts found in Motorola low-rise digital systems, the specified transmission is a 216-bit payload and 48-bit synchronous or embedded signaling. It takes 27.5 milliseconds to transmit this specified transmission, and in actual transmission, there is a guard time of 1.25 milliseconds on either side. Therefore, in such a Motorola low-rise digital system, the "burst" is 30 milliseconds.

( "Cha in the art wireless medium for voice communication before accessing known as Channel"), consider the modes SU voice communication requested requires. For example, the SU transmits voice communications in repeater mode or talkaround mode. If the requested voice communication requires repeater mode, the SU requires BR to complete the voice communication. In one exemplary embodiment, repeater mode is defined as SU voice transmission in which the SU transmits to the BR at uplink frequencies to provide RF energy. The BR then transfers the voice transmission to the downlink frequency to supply RF energy to the target SU. If the requested voice communication requires talkaround mode, the SU does not require BR to complete the voice communication. In one embodiment of the example, talkaround mode is defined as SU voice transmission in which the SU transmits to the target SU at a downlink frequency to provide RF energy. As is known in the art, talkaround mode is also known as direct mode and is characterized as SU audio transmission that SU transmits at downlink frequencies without the assistance of BR.

In one exemplary embodiment, RF energy may be supplied by SU or BR. Supplying here means transmitting on a channel. In addition to this, the communication between SU and BR may be voice or data / control. Therefore, there are four types of communication on the channel: voice supplied by SU, data (/ control) supplied by SU, voice supplied by BR, and data (/ control) supplied by BR. Exists. In order to understand what type of communication is transmitted in the SU or BR receiver and process the communication appropriately, the communication has a 48-bit (24 symbols) frame synchronization word to identify the communication type. included.

Before accessing the voice communication channel, the SU considers the supplied characteristics of the SU. A SU supply characteristic is a programmed attribute or function that tells the SU how to operate. In one exemplary embodiment, customer-supplied software (CPS) (also known as wireless service software (RSS)) manufactured by Motorola is used to assign supply characteristics to the SU. For example, the SU can access the channel with a supply characteristic of "polite". Here, "polite" means to consider what type of communication currently exists on a channel before the SU accesses the channel for its own communication. In one typical embodiment, being "polite" means being "polite" for all voice communications on the channel and other voice communications on the channel from other SUs with the same color code. It can be further divided into being "polite" only for. A SU that is "polite" to all means that the SU is "polite" to any detected channel activity.

SU has an "impolite" supply characteristic if it is not "polite". Here, "rough" means that the SU initiates its transmission without first confirming that the channel is available and clear. In one typical embodiment, "emergency" communication is a type of "rough" communication.

As is known in the art, a "color code" is a common identifier used by a group of SUs that utilize the same BR. For example, as shown in FIG. 1, SU12,14,22 use the same BR, that is, BR9, so that the color codes are the same. In addition, color code fields may be present in embedded signaling messages and general data bursts to provide a means of handling wireless networks or specific repeaters so that co-channel interference is eliminated. Further, as is known in the art, a "talk group" is a group of SUs that share an RF frequency and time slot and have the same color code. In one exemplary embodiment, talk groups are identified by a 16-bit talk group identifier (TGID) and individual subscriber devices are identified by a 24-bit subscriber device identifier (SUID). Therefore, in one embodiment of the example, SUs that share a color code are further divided into talk groups so that SUs in one talk group do not hear SUs in another talk group.

In one typical embodiment, the SU, which is in direct mode and has a "rough" supply characteristic, does not consider whether the channel is busy or not, or other channels. Have access to the channel and transmit voice communications without considering factors.

In one typical embodiment, the SU, which is in direct mode and has a supply characteristic that is "polite" to everything else regardless of color code, has access to the channel unless there is RF energy on the channel. Is allowed. The term "RF energy on a channel" means that the RF energy on the channel exceeds the threshold provided in the SU. Therefore, in one typical embodiment, the SU is prohibited from accessing the channel when the measured RF energy level on the channel is greater than the CPS characteristic value for channel access. In addition to this, if the SU is a participant in the call, the SU is allowed to send "roughly". Here, roughly, means that the SU starts transmission at the beginning of voice transmission.

In one typical embodiment, a SU that is in direct mode and has a supply characteristic that is "polite" to a SU with the same color code will have audio transmission on the channel in the absence of RF energy on the channel. Access to the channel is allowed unless it matches the SU color code. Therefore, the SU considers the presence of RF energy on the channel and determines the color code of the voice transmission before allowing or rejecting the requested voice transmission. Such transmission requires time slot synchronization to determine the color code of the audio transmission on the channel. In addition to this, if the SU is a participant in the call, the SU is allowed to send "roughly". Here, roughly, means that the SU starts transmission at the beginning of voice transmission.

In one typical embodiment, a SU that is in repeater mode and has a supply characteristic in which the SU is "rough" for voice communication on the channel synchronizes to the BR downlink before allowing voice communication and is correct. Ask the SU to check the color code and identify the TDMA channel. In one typical embodiment, if the BR is not in an awake state, more specifically if the BR downlink is not active, synchronization to the BR requires the execution of a BR wakeup procedure. SUs that are in repeater mode and have a "rough" supply characteristic do not provide protection for calls, ie transmissions on the channel. Therefore, regardless of whether the voice transmission is analog or digital, has the same color code, or has the same call, a "coarse" SU is placed on its own communication channel. to access.

In one typical embodiment, if the SU is in repeater mode and the SU has a supply characteristic that is "polite" for all voice communications on the channel, the SU will only take into account the state of the channel. Access to is granted. If the SU is in repeater mode and is "polite" for all voice communications, the transmissions of co-channel users are whether those transmissions are analog or digital, and whether they have the same color code. Protected whether or not they are the same call. In addition to this, if the SU is a participant in an ongoing call, the SU is allowed to send "roughly". Here, roughly, means the "first" of active transmission in progress. If the SU is not a participant in an ongoing call, the SU will not be granted access to the channel. Such combinations, which require consideration of the presence of RF energy on the channel during operation, require BR downlink synchronization to provide the correct color code before accessing the voice communication channel. Check and identify the TDMA channel. In addition, if the BR is not awake, and more specifically if the BR downlink is not active, synchronization to BR requires a BR wakeup procedure to be performed.

In one typical embodiment, a SU that is in repeater mode and has a supply characteristic that is "polite" for the same color code allows the SU to access the radio channel only after considering the state of the channel. To do. Such a combination protects digital co-channel users who use the same color code. In addition to this, if the SU is a participant in any ongoing call or transmission, the SU is allowed to send "roughly". Similar to the situation described above where the SU is in repeater mode and has a "rough" supply characteristic, the SU considers RF energy detection before allowing voice transmission, synchronizes to the BR downlink, and has the correct color code. Is required to identify the TDMA channel. In addition, if the BR is not awake, and more specifically if the BR downlink is not active, synchronization to BR requires a BR wakeup procedure to be performed.

Referring to FIGS. 2-4, during operation, the subscriber device is in an awake state and needs to request access for voice transmission. As shown in FIG. 2, the subscriber device requests voice transmission by pressing PTT (block 202). If the PTT is pressed, the SU checks to see if the SU is a participant in the ongoing call (block 203). If the SU is a participant in an ongoing call (block 203), the SU is allowed access to the voice transmission channel (block 416). If the SU is not a participant in an ongoing call and the SU is not yet awake (block 204), the SU must be awake (block 208). If the SU is in the awake state, a determination is made as to whether the SU is scanning the RF channel (block 206). If the SU is scanning, the SU stops scanning and adjusts to a specific frequency to request audio transmission (block 210). If the SU is not scanning, processing continues.

The SU then requests voice transmission. When the SU requests voice transmission in direct mode, which does not require repeaters for communication (block 212), the SU monitors the channel for RF energy (block 214). Direct mode is also known as talkaround mode. If the SU requests voice transmission that is not in direct mode (also known as repeater mode) (block 212), the SU monitors the channel for RF energy (block 222). In one exemplary embodiment, in direct mode the SU transmits at the downlink frequency using the synchronization supplied by the SU, and in repeater mode the SU uses the synchronization supplied by the SU to transmit at the uplink frequency. Send with.

In direct mode, when the RF energy threshold is exceeded (block 214), the SU searches for synchronization and color code information. For further description, refer to the above description of synchronization and color coding. From synchronization and color code information, the SU determines if the voice transmission is a non-emergency call and is being fed to "polite" channel access (block 216). In addition, if this "polite" channel access specifies that the SU is "polite" for all (block 218), the SU sends negative feedback to the SU user (block 220). Therefore, voice transmission is not transmitted over the radio channel. Instead, if this "polite" channel access specifies that the SU is "polite" for its own color code rather than "polite" for all (block 218), Figure 3 As shown in, SU determines if the time slots are synchronized (block 302).

In addition, if in direct mode and the RF energy threshold is not exceeded (block 214), the SU is ready to transmit (block 418), as shown in FIG. Also, in direct mode, when the RF energy threshold is exceeded (block 214) and the voice transmission is an emergency call or the voice transmission is "rough" (block 216), as shown in FIG. , SU is allowed to perform voice communication using wireless channels (block 418).

In repeater mode, the BR must be awake (block 224) if the RF energy threshold is not exceeded and the base repeater (BR) is not yet awake. The SU initiates the wakeup procedure (block 224) and sends a 1-slot wakeup message to BR (block 228). This wakeup message is an idle message that carries synchronization and color code information. BR confirms that the color code is correct and activates the downlink. Therefore, as shown in FIG. 2, if the BR is not keyed, that is, if the wakeup procedure does not succeed in waking the BR, the voice transmission request is not allowed. If the BR wakeup attempt is unsuccessful after two attempts (block 226), the SU user is given negative feedback (block 230).

In addition, in repeater mode, when the RF energy threshold is exceeded, the SU determines if the time slots are synchronized, as shown in FIG. 3 (block 302). Again, as mentioned above, the SU searches for synchronization and color code information when the RF energy threshold is exceeded.

Now referring to Figure 3, the SU first checks to see if the communication between the SU and BR is synchronized. If the communication between SU and BR is out of sync, SU attempts to perform synchronization (block 304). After attempting synchronization (block 304), the SU checks the mode (block 308), checks the type of communication (eg emergency, non-emergency, etc.) (block 310), and types of "politeness" (eg, politeness). Inspect all for "polite", own color code for "polite", "rough", etc.) (blocks 310, 312). It is not possible for the SU to synchronize the communication between the BR and the SU, and when checking the above parameters, the user is given negative feedback (block 314).

In one typical embodiment, performing synchronization between BR and SU (block 304) involves waiting for a predetermined period of time to detect a time slot synchronization signal. The time slot sync signal is a 48-bit (also known as 24 symbols) frame sync word. For a single time slot, the time slot sync signal is available every 360 milliseconds during a voice call, during call hang times, channel hang times, and other conditions including during data transmission. , May be available every 60 milliseconds. The execution of synchronization (block 304) is completed by detecting the time slot synchronization signal within a predetermined period (block 306).

If the communication between SU and BR is synchronized (block 302), or if SU is able to successfully perform synchronization between BR and SU (block 304), then the SU is TDMA. Recover the color code from the channel (block 316). In one typical embodiment, the recovered color code is available for each burst other than bursts, including voice synchronization. Further, in one typical embodiment, the SU matches the recovered color code twice with the color code supplied by the SU before it is said that a match has occurred (block 318). In the SU, if the recovered color code matches the color code supplied by the SU (block 318) and the SU is in direct mode, the SU is not allowed to send and negative feedback is given to the SU user. Given (block 324). If in direct mode (block 320) and the recovered color code does not match the color code supplied by the SU (block 318), the SU will use the wireless channel for voice communication, as shown in Figure 4. Allowed to run (block 418).

Looking here at Figure 4, there are some situations where negative feedback is given to SU users (blocks 408,420). In one situation the SU is in repeater mode, detects RF energy and is synchronized with the BR, the recovered color code matches the supplied color code, but either time slot is 1 and It is not possible for the SU to identify which time slot is 2 within a given time period (block 404). The SU determines the time slot number by decoding the TDMA channel field of the Common Announcement Channel (CACH) message. In one typical embodiment, the SU matches the TDMA channel field of the CACH message twice before the time slot number is determined (block 404). If the SU is unable to determine the time slot number within a given time period (block 406), negative feedback is given to the SU user (block 408).

In addition to this, when the SU determines that the voice transmission is a non-emergency call and is being supplied for "polite" channel access (block 410), when the time slot is used for system-wide communication. Negative feedback is given to the SU user (block 416), or when the time slot is used by another SU and is busy (block 414). In all other cases, the SU is allowed to perform voice communication over the wireless channel (block 418). For example, if a "polite" SU activates the emergency function of that SU, the SU acts "roughly" and has access to the channel.

In allowing the SU to transmit voice (block 418), the SU may determine if the target time slot is idle (block 412). If the channel state field in the CACH message indicates an idle channel, then the target time slot is considered idle. Further, when the SU determines whether the time slot is used for system-wide communication (block 416), the SU first determines whether the time slot is idle or busy. This is done by decrypting the access type field of the CACH message (block 412). If the access type field indicates that the time slot is idle, the SU verifies another CACH message and checks the access type field to confirm that it is idle. If the access type field indicates that the time slot is not idle, the SU determines if the SU is a participant in an activity on the time slot (block 414). The SU determines whether or not the SU is a participant in the activity by observing the link control information on the channel. If the link control information indicates that the SU is not a participant in the activity, the SU determines if the activity on the time slot is being used for a system-wide activity. If the activity on the time slot is not system-wide activity (block 416), the SU is granted access to the audio transmission channel (block 418).

When the SU finishes the voice transmission, the BR sends a hang time message. Here, the hang time is defined as the period starting from the end of the SU voice transmission and there is no activity on the uplink. SUs are given the opportunity to request channel access during hang times and take advantage of the uplink idle state. In one typical embodiment of the invention, the conventional hang time period is divided into a call hang time period and a channel hang time period. As used herein, the call ends when the BR transitions to a channel hang time, when the BR unlocks, or when the channel is overtaken by a "rough" transmission.

During the call hang time, BR sets the channel state bit busy, even when the uplink is not busy. In addition, BR sends link control information to advertise that the SU, who was a participant in the call, may override the channel state bits and access the voice transmission channel. In addition, the BR is already keyed, so the SU does not need to awaken the BR. Specifically, the SU who was a participant in the call can access a new channel for voice transmission that is not related to the previous call without having to initiate the BR wakeup procedure. The call hang time begins at the end of the SU voice transmission and ends when the channel hang time begins. In one typical embodiment, the call hang time follows the call for a few seconds, for example 3 seconds.

During channel hang time, BR sets the channel state bit to idle, allowing any SU to access the channel without first transmitting a BR wakeup sequence. The BR does not need to be awakened by the SU because the BR is already keyed. Therefore, SUs seeking access to the channel save time by not having to awake BR. During channel hang time, BR sends an idle TDMA burst to ensure that the channel is not in use and is not reserved for use. The channel hang time is defined as the period that begins at the end of the call hang time and ends when the BR unlocks when the SIT expires. In addition, the SIT covers the call hang time plus the channel hang time. In one typical embodiment, the channel hang time starts at the end of the call hang time and lasts for a few seconds, eg 2 seconds.

In one typical embodiment of the invention, the SU considers hang times and "politeness" before accessing the channel. Specifically, during the call hang time, the SU who is the participant of the call will be on the channel regardless of whether the SU is provided with "polite" channel access or "rough" channel access. You may access it. Therefore, if the SU who is a participant in the call receives an indication that the channel is in the call hang time, the SU can request access to the channel. On the other hand, if the SU is provided with "polite" channel access, the SU that is not a participant in the call does not have to send during the call hang time. Therefore, the SU who is a participant in the call is first offered the opportunity to continue the call before another call is allowed to be initiated on the channel.

For "rough" channel access, the SUs supplied with "rough" channel access are a) during active transmission by another SU, b) during call hang time, c) during channel hang time, and d) Voice transmission can be started at any time, even if the BR is not in an awake state. Therefore, SUs supplied with "rough" channel access ignore the channel state field in CACH messages and do not attempt to distinguish between call hang times and channel hang times.

Therefore, the present invention allows the SU to consider the actual situation on the channel before voice transmission occurs. This often reduces the time it takes to access the channel. In addition to this, the present invention protects the continuity of ongoing calls by reducing the likelihood that the call will be interrupted by a SU that is not a participant in the call but has the same color code.

<figref num="1">The block diagram of the typical one wireless communication system by one Embodiment of this invention.</figref><figref num="2">Flowchart of a typical method for providing channel access for voice transmission.</figref><figref num="3">Continuation of the flowchart of a typical method shown in Fig. 2.</figref><figref num="4">Further continuation of the flowchart of a typical method shown in FIGS. 2 and 3.</figref>