In: Root » Electronics and communication » Wireless and mobile computing
The need for increased capacity was the great motivation for the advent of American digital cellular technology. As demand for wireless services increased, mainly in dense urban areas, the old analog standard, known as AMPS (Advance Mobile Phone Service), proved inadequate to satisfy the demand. Time Division Multiple Access technology, based on the EIA/TIA/IS- 54 specifications (later on enhanced and renamed EIA/TIA/IS-136) was the first solution to the capacity problem of the old analog system. By offering roughly a threefold increase in capacity by dividing each 30 kHz AMPS channel into three time slots, this system was the first American response to the European cellular second generation, the GSM. This digital novelty, however, was not enough to soothe a number of service providers, who argued that such a technology would not be adequate for future growth in service. Other alternatives were then considered, and a technical committee was formed to study and generate cellular standards for wideband services. In the late 1980s and early 1990s, QUALCOMM, Inc. of San Diego proposed a Code Division Multiple Access, CDMA, system and together with Pacific Telesis demonstrated its operation. Extensive successful field trials and network refinement led the Telecommunication Industry Association (TIA) and the Electronic Industry Association (EIA) to adoptQUALCOMMsystem as their interim standard, the “TIA/EIA/IS-95— Mobile Station–Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System.” The TIA/EIA/IS-95 specifications establish that the system operate on a dual-mode (analog and digital) basis, both modes within the same frequency band. The dual-mode capability facilitates the transition from the analog environment to a digital environment. Although compatible, analog and digital systems are rather different. TIA/EIA/IS-95 supports a direct sequence spread spectrum technology with 1.25 MHz band duplex channels. Therefore, an operating company that chooses this CDMA technology must deactivate about 42 contiguous 30-kHz channels of its analog system. Coexistence of analog and digital systems implies that dual-mode mobile stations are able to place and receive calls in any system and, conversely, all systems are able to place and receive calls from any mobile station. Handoff operations in such a scenario require some attention. A mobile station may initiate a call in the CDMA system and, while the call is still in progress, it may migrate to the analog system, if required. The search for one or another system for the initial registration is not specified by the standard and the exact action is dependent on the manufacturer. In fact, the standard leaves a number of issues to be detailed by the manufacturer. Those recommendations in the standard appearing with the verbal forms “shall” and “shall not” identify the requirements from which no deviation is permitted. Those with “should” and “should not” indicate that several possibilities are permitted. There are still others with “may” and “need not” and “can” and “cannot,” which are certainly much less restrictive. Therefore, solutions may be implemented differently by different manufacturers. A number of innovations have been introduced in the CDMA system as compared with earlier cellular systems. Soft handoff is certainly a great novelty. In soft handoff, handoff from one base station to another occurs in a smooth manner. In soft handoff, the mobile station keeps its radio link with the original base station and establishes a connection with one or more base stations. The excess connections are given up only when and if the new link has sufficient quality. Another innovation introduced in the CDMA system is the use of Global Positioning System (GPS) receivers at the base stations. GPSs are utilized so that base stations be synchronized, a feature vital to the soft handoff operation. Vocoders at variable rates are specified to accommodate different voice activities aimed at controlling interference levels, thence increasing system capacity. Sophisticated power control mechanisms are used so that the full benefit of spread spectrum technique is realized. The firstCDMAsystems were employed under the TIA/EIA/IS-95A speci- fications. The A version of the specifications evolved to TIA/EIA/IS-95B, in which new features related to higher data rate transmission, soft handoff algorithms, and power control techniques have been introduced. The name cdmaOne is then used to identify theCDMAtechnology operating with either specification. Features and Services TIA/EIA/IS-95 specifications establish two types of features: voice features and short message service features. Voice Features The following are the primary voice features. Call Delivery (CD).CDallows the reception of a call while in a roaming condition. Call Forwarding Busy (CFB)/Call Forwarding Busy No Answer (CFNA)/ Call Forwarding Busy Unconditional (CFU). CFB, CFNA, and CFU allow a called subscriber to have the system send incoming calls, addressed to the called subscriber’s directory number, to another directory number (forward-to number), or to the called subscriber’s designated voice mailbox. This happens when the subscriber is engaged in a call or service (for CFB active), or when the subscriber does not respond to paging, does not answer the call within a specified period after being alerted, or is otherwise inaccessible (CNFA active). The inaccessibility may be characterized by the following: no paging response, unknown subscriber’s location, inactive subscriber, CD not active for a roaming subscriber, Do Not Disturb active, etc. If CFU is active, calls are forwarded regardless of the condition of the termination. Call Transfer (CT). CT enables the subscriber to transfer an in-progress established call to a third party. The call to be transferred may be an incoming or outgoing call. CallWaiting(CW).CWprovides notification to a controlling subscriber of an incoming call while the subscriber’s call is in the two-way state. Subsequently, the controlling subscriber can either answer or ignore the incoming call. If the controlling subscriber answers the second call, it may alternate between the two calls. Calling Number Identification Presentation (CNIP)/Calling Number Identification Presentation Restriction (CNIR). CNIP provides and CNIR restricts the number identification of the calling party to the called subscriber. The termination network receives the calling number identification (CNI) as part of the basic call setup. This CNI may include one or two calling parties numbers (CPNs), a calling party © 2002 by CRC Press LLC subaddress (CPS), redirecting numbers (RNs), and a redirecting subaddress (RS). Conference Calling (CC). CC provides a subscriber with the ability to conduct a multiconnection call, i.e., a simultaneous communication between three or more parties (conferees). If any of the conferees to a conference call disconnects, the remaining parties remain connected until the controlling subscriber disconnects. Do Not Disturb (DND). DND prevents a called subscriber from receiving calls. When this feature is active, no incoming calls shall be offered to the subscriber.DNDalso blocks other types of alerting, such as the CFU abbreviated (or reminder) alerting and message waiting notification alerting. DND makes the subscriber inaccessible for call delivery. Flexible Alerting (FA). FA causes a call to a pilot directory number to branch the call into several legs to alert several termination addresses simultaneously. The first leg to be answered is connected to the calling party and the other call legs are abandoned. Message Waiting Notification (MWN). MWN informs enrolled subscribers when a voice message is available for retrieval. MWN may use pip tone or alert pip tone to inform a subscriber of an unretrieved voice message(s). Mobile Access Hunting (MAH). MAH causes a call to a pilot directory number to search a list of termination addresses for one that is idle and able to be alerted, in a way that only one termination address is alerted at a time. Password Call Acceptance (PCA). PCA is a call-screening feature that allows a subscriber to limit incoming calls to only those calling parties who are able to provide a valid PCA password (i.e., a series of digits). Preferred Language (PL). PL provides the subscriber with the ability to specify the language for network services. Priority Access and Channel Assignment (PACA). PACA allows a subscriber to have priority access to voice or traffic channels on call origination by queuing these subscribers’ originating calls when channels are not available. The subscriber is assigned one of several priority levels and the invocation ofPACAis determined to one of two options: permanent, in which the feature is always available, and demand, in which the feature is available only on request. Remote Feature Control (RFC). RFC allows a calling party to call a special RFC directory number to specify one or more feature operations. Selective Call Acceptance (SCA). SCA is a call-screening service that allows a subscriber to receive calls only from parties whose CNPs are in an SCA screening list of specified CNPs. Subscriber PIN Access (SPINA). SPINA allows subscribers to control whether their mobile station is allowed to access the network. This feature may be used by subscribers to prevent unauthorized use of their own mobile station or fraudulent use by a clone. Subscriber PIN Intercept (SPINI). SPINI enables subscribers to restrict outgoing calls originated from their mobile station. The subscriber requires a SPINI PIN authorization code to originate calls meeting specified criteria (e.g., international call type). SPINI PIN shall not be required on unrestricted call types (e.g., emergency) and may not be required for a list of frequently called numbers, regardless of their call type. Three-Way Calling (3WC). 3WC provides the subscriber with the ability to add a third party to an established two-party call, so that all three parties may communicate in a three-way call. Voice Message Retrieval (VMR). VMR permits a subscriber to retrieve messages from a voice message system (VMS). Voice Privacy (VP). VP provides a degree of privacy for the subscriber over the base station to mobile station (BS–MS) radio link. Short Message Service Features The following are the primary short message service features: Short Message Delivery–Point-to-Point Bearer Service (SMD-PP). SMDPP provides bearer service mechanisms for delivering a short message as a packet of data between two service users, known as short message entities (SMEs). The length of the bearer data may be up to 200 octets. Implementations and service providers may further restrict this length. The SMD-PP service attempts to deliver a message to an MS-based SME whenever the MS is registered even when the MS is engaged in a voice or data call. Cellular Paging Teleservice (CPT). CPT conveys short textual messages (up to 63 characters) to an SME for display or storage. Cellular Messaging Teleservice (CMT).CMTconveys and manages short messages to an SME for display or storage. This teleservice should coordinate the use of the display and arbitrate between conflicting users or services. Each message includes attributes for management of the messages received by the SME.
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