Compressed voice data and targeted delivery for narrowband PCS paging
The paging system architecture components referred to by common terms in this article are trademarked by Motorola under the following names: Flex_the overall family of paging protocols, standing for flexible, asynchronous, wide-area paging protocol. Inflexion_two-way voice paging protocol. Wireless Message Gateway (WMG) Terminal_paging entry service terminal. RF-Conductor_paging system controller. RF-Orchestra_over-the-air paging transmitter. RF-Audience_over-the-air paging receiver. Tenor_voice pager.
Compression of voice pages allows a greater number of them to be transmitted over the available RF bandwidth. Operators can place more subscribers into service by using targeted delivery techniques to maximize system resources.
Voice paging has been around in previous forms for specialized applications. With the narrowband PCS that has become available from the 1996 PCS auctions, providers are able to commercialize voice paging for mass-market applications. This has been enabled by new technologies and delivery approaches that are being used in the paging industry.
The key technology that permits voice paging to occur is the two-way voice paging protocol within Motorola’s family of wide-area paging protocols. The protocol provides for two-way operation and voice message delivery.
Service concept The simplest way to view voice paging is as an answering machine on a belt or in a purse. In normal operation, voice messages are delivered to the paging device and stored until the subscriber desires to listen to the message. After hearing the messages, subscribers have the option of saving or deleting the messages.
The obvious improvement to the answering machine paradigm is the wireless nature of the service; subscribers have near-immediate availability of the message. This solves the dilemma of access to the wireline answering machine that requires subscribers to periodically “call in” to check for messages. This change in delivery approach permits subscribers to more promptly respond to their messages.
System architecture The architecture of the voice paging infrastructure, as shown in Figure 1 below, looks similar to the traditional one-way paging system. However, there are differences. Support for the voice data imposes numerous loading and bandwidth demands on the system components. The page entry terminal used in one-way paging continues to do so with voice paging. However, the voice is collected, digitized, stored and used differently than messages for traditional one-way numeric or alphanumeric pages. In fact, the voice message is collected in a manner comparable to wireline voice mail. However, the paging voice data compression factor plays a much greater role than in voice mail because of the multiple transmissions required for delivery.
The system controller handles the message delivery process. It formats and schedules control messages and then delivers the voice message using the appropriate transmission facilities. The paging transmitter sends the message over the air to the pager. The paging receiver accepts the messages sent by the pager and sends them on the system controller. The subscriber’s voice pager for the system is not only able to store multiple messages but also permits the subscriber to play, replay, fast-forward and delete messages. As with other pagers, the voice pager alerts the subscriber of incoming messages using either tone or vibration.
Infrastructure support A crucial aspect of the infrastructure is its ability to move the data for the voice message to where it is needed, when it is needed. Several factors must be considered: * Data compression. * Frequency reuse. * Data flow management. * Compression of voice data _ For a given operator, the least tolerant constraint that influences system design is the amount of available RF spectrum. Only so much is available, and adding spectrum can be extremely expensive. As a result, efficient use of this finite resource is critical.
Compression of the voice data allows a greater number of voice messages to be transmitted over the available RF bandwidth. This, in turn, lets an operator place more subscribers into service. An additional benefit is the reduced storage requirements needed to hold messages, pending delivery.
The compression of voice data permits the information to be sent to the pager with minimum latency. For example, a 15-second voice message that has undergone compression can be delivered to the pager using less than 3.5 seconds of airtime.
Although voice compression can be seen to improve airtime use, it also helps reduce network costs. These can be seen directly as costs associated with storage space and networking bandwidth required for each message.
* Frequency reuse _ The protocol subdivides the frequency spectrum into subchannels. This permits adjacent cells to be transmitting messages to separate paging subscribers at the same time without the cells interfering with each other. Over larger areas, these subchannels can be reused. This permits many separate messages to be transmitted at the same time. This is how voice paging can provide service for a larger number of subscribers.
With the additional subscribers, the paging infrastructure must deliver more messages. This delivery process involves moving data from the home terminal to the controllers and then to the transmitters. As RF efficiency improves and frequency reuse permits more messages to be delivered, the supporting network must be able to handle increasing network loads.
* Data flow in the paging network _ Even with compressed voice data, excessive or unneeded movement of the data through the network is a wasteful activity that ultimately affects system performance or incurs additional cost. Therefore, strategies exist that attempt to guarantee that only necessary data is moved.
In a traditional, one-way paging network, paging messages are sent from the terminal to appropriate controllers that transmit the data for the subscribed serv-ice area. The data is moved for a minimal period, and the basic theory of operation is “Send it, and they will get it_if they are where they are supposed to be.” In two-way paging_especially voice paging, which provides for guaranteed delivery_the data is not sent until the pager is located and is prepared to receive the transmission. This paradigm can be used to control the movement of the data in the network.
Until the pager is available and ready, the data need not be sent to the transmitter for transmission. Further, the data need not be delivered to any controller except the one that operates the transmitter for the cell where the pager will be receiving the message. These simple principles can be used to control the data movement and, therefore, the ancillary costs involved in transporting the massive flow of voice data these systems will be handling.
Paging protocol capabilities The efficiency sought from the infrastructure is supported by specific capabilities of the two-way voice paging protocol. In particular, delivery control is a key feature of the protocol that permits network operational behaviors to be implemented directly. To describe this feature, some background information about the protocol is needed.
* Communication channels _ The delivery of voice messages involves several communications between the voice pager and the infrastructure. These transmissions occur over three separate logical channels: * Forward paging control channel. * Forward voice channel. * Reverse channel.
The forward paging control channel carries the protocol’s control messages. This channel is broadcast over a region in a fashion similar to traditional one-way simulcast transmissions. Messages sent on this channel would address those pagers that are registered in the region.
The forward voice channel is used to transmit the voice data. This channel is not simulcast by multiple transmitters. Each transmitter has its own data to be delivered. Multiple voice channels can be carried in the RF spectrum used by the control channel. Additional spectrum allows for even more available voice channels. These voice channels permit frequency reuse patterns to be established in adjacent transmission areas.
The reverse channel is used by the pager to communicate to the system for message and command acknowledgments. It uses different frequencies than the forward channels.
Pagers monitor the control channels to be informed of voice messages to be delivered. When all is ready, the pager receives its message from the assigned voice channel. When the message has been received, the pager reports its status to the system.
* Targeted delivery _ Efficient use of the RF spectrum is supported by selective transmission of the “bulky” voice message to the smallest possible area. Sending such data in a large simulcast area would be wasteful of the available bandwidth. Therefore, the protocol enables targeted delivery.
The key to targeting message delivery is “knowing” where the pager is located. This knowledge is maintained using a hierarchical location model. At the highest level, terminals maintain information about the pager’s location to the zone level. This information is acquired through the zone registrations that pagers perform when they move from one zone to another.
At a middle level in the location hierarchy, a zone may be subdivided into multiple subzones. The division of zones into subzones is managed by the controller. Such dividing is performed, as needed, to support larger population densities. Depending on system requirements, a pager can be instructed to perform location registration as it crosses subzone boundaries. Information related to such crossings is maintained in the controller and is not communicated to the terminal.
The lowest level of the location model is the identification of the “current” transmitter from which the pager can receive a page. This information is only acquired when needed and is not maintained beyond its immediate need. The primary need for this information is in the delivery of voice messages to the pager.
When a new voice message is received by the terminal, it uses its zone information to inform the controller of the need to deliver the message. The controller then uses any associated subzone information to determine where it will look for the pager. This is accomplished with a “WhereAreYou” command. The pager responds to this inquiry, as scheduled, with information regarding the transmitter from which it received the request. The controller uses the transmitter information in scheduling and broadcasting the actual voice data. The voice data is transmitted on a voice channel of the useful transmitter.
Figure 2 above shows a scenario where two separate pagers, in the same zone, are queried and sent their pages. The patterned areas show the coverage of the specific transmitter that each pager reports “hearing.” These would be the transmitters used for the targeted deliveries.
Summary The success of voice paging will be partly determined by the efficiency of the data movement through the supporting infrastructure. The initial operators using this protocol (PageNet in the United States and Amtel in Puerto Rico) are commercially operating and validating the success not only of the voice service itself but also of the network infrastructure needed to support it. Lasting innovations in two-way paging will undoubtedly be made in the quest for continued improvement in this dynamic arena.
As two-way voice paging develops, productivity tools for alphanumeric, multisite paging also continue to improve. Silverlake Communications, Calabasas, CA, has developed wireless PCS messaging software, under the name Airsource Business Suite, that is compatible with alphanumeric pager services and PCS providers supporting text messages to their devices. The program allows a network administrator to configure an email address, such as “pager,” to send text to a pager through a wireless gateway. Alan Gould, director of business development for Silverlake, has compiled the following “Top ten reasons why messaging software contributes to productivity:”
* Updated, critical or time-sensitive information can be sent to one pager or an entire organization instantaneously. * Accuracy of alphanumeric messages can be increased through bypassing operator-assisted services and the optional use of a spell-checker. * Message senders can send pages from their PC workstation instead of having to change position to a hardware alpha-entry device. * Dispatch time is reduced by direct dialing into the message carrier. * Confirmation is given that the message was sent and received successfully, allowing the message to be re-sent or re-routed if not received. * Storage and instant access to frequently used or repeated messages is available. * All pager information is stored in a central database, eliminating the need to look up or memorize messaging carrier information, PINs, access numbers or group codes. * Text pages can be linked to existing email programs. * Delivery scheduling can be arranged for text pages, such as reminders or appointments. * Management and tracking of pages through a log, or hard copy, allows both the sender and the recipient to keep records.
Paging is becoming increasingly interconnected with other forms of information flow because of the efficiency and mobility of wireless communication. Software producers are creating programs that establish an interface with workstations and networks. Telamon, Oakland, CA, has created an updated version of its Telalert product for general-purpose voice notification and response. The new release supports a variety of UNIX and NT platforms. The program was originally designed to send pager notifications to support personnel about system or network problems detected by management platforms or help-desk applications. Applications now extend to interactive voice response; electronic sign messaging; modem, email and voice mail; and the relaying of alerts to and from alarm systems. Capabilities added to Telamon’s system include support for Skytel’s two-way paging and other PCS services that allow field personnel to acknowledge receipt of a trouble ticket and respond to the software without any operator intervention.
In addition to interactive voice, alphanumeric and two-way paging, the software also supports PCS, landline, cellular services and Simple Network Paging Protocol (SNPP). Two other supported functions are escalation and resource scheduling. Fail-safe escalation allows unacknowledged messages sent to paging, voice mail or some other medium to be re-sent using one of the other alternatives, depending on the urgency. Resource scheduling allows the unavailability of the recipient to be considered, based on vacation schedules, off-site work or other conditions. The program won’t waste time looking for someone who is not available.
