Spatial Division Multiple Access (SDMA) & Third Generation Wireless (3G) | Future Enhancements

Some of the key future enhancements to wireless technology include spatial division multiple access (SDMA) and the introduction of third generation (3G) wireless technologies.

Spatial Division Multiple Access (SDMA)

Spatial division multiple access (SDMA) is a system access technology that allows a single transmitter location to provide multiple communication channels by dividing the radio coverage into focused radio beams that reuse the same frequency. To allow multiple accesses, each mobile radio is assigned to a focused radio beam. These radio beams may dynamically change with the location of the mobile radio. SDMA technology has been successfully used in satellite communications for several years.

Figure 1 shows a SDMA system. This diagram shows a single tower that is serving 3 different users from the same radio tower on the same frequency using independent beams of radio energy.

Figure 1: Spatial Division Multiple Access (SDMA)

Third Generation Wireless (3G)

Third generation wireless (3G) is a term commonly used to describe the third generation of technology used in a specific application or industry. In cellular telecommunications, third generation systems used wideband digital radio technology as compared to 2nd generation narrowband digital radio. For third generation cordless telephones, products used multiple digital radio channels and new registration processes allowed some 3rd generation cordless phones to roam into other public places.

The 3G system is actually the universal mobile telecommunications System (UMTS). The UMTS system offers personal telecommunications services that use the combination of wireless and fixed systems to provide seamless telecommunications services to its users. The UMTS allows bandwidth on-demand transmission capacities of up to 2 Mb/s in some of its radiolocations. It should be compatible with GSM and broadband ISDN systems.

Figure 2 shows a 3rd generation broadband wireless system. This system uses two 5 MHz wide radio channels to provide for simultaneous (duplex) transmission between the end-user and other telecommunication networks. There are different channels used for end- user to the system (called the “uplink”) and from the system to the end-user (called the “downlink”). This diagram shows that 3G networks interconnect with the public switched telephone network and the Internet. While the radio channel is divided into separate codes, different protocols are used on the radio channels to give high priority for voice information and high-integrity to the transmission of data information.

Figure 2: 3rd Generation Wireless

Wireless Data & Broadcast Television | Services

Wireless Data

There are three basic services offered by wireless data systems: circuit switched data, packet switched data and messaging.

Circuit switched data is a bearer service as it only transports the user’s data between points. When sending data through a circuit switched connection, the user regularly pays a standard per-minute charge for the amount of time that the connection is maintained regardless of how much data is sent through the channel.

It usually takes approximately 10 to 20 seconds to establish a circuit switched connection on a wireless network. This is due to the processing of dialed digits through the telephone network and the amount of time the modem requires to establish which communication language will be used (called training time). The user ordinarily pays for this setup time even if they only have a very small amount of information to send (such as an email message). Once a connection is established on a circuit switched connection, data transfer rates generally range from 9600 bps up to 28,800 bps.

Packet switched data is also a bearer type of service as it only transports the users data between points. When sending packets of data through the network, the user normally pays only for the amount of data or number of packets that they send.

Unlike circuit switched data, the connection time for packets is ordinarily under 1 second (some systems may be below 150 msec) and the user does not pay for this setup time. The typical price for packet data transmission ranges from approximately 4 cents to $1 per kilobyte. A one-time activation fee is as a rule required along with a minimum monthly fee. The usage amount is normally applied to the monthly fee.

Several wireless data service providers in the United States now offer service based on application and number of units. This results in different price plans that can vary from $15-25 per month per unit with some systems offering a flat fee for a fixed or unlimited amount data transmission. The trend is to move away from the per packet charge.

Figure 1 shows a typical wireless packet data rate plan. This table shows that there is usually a monthly recurring fee that provides the user with a monthly amount of data. If the customer uses the maximum data allocation, an additional fee per kilobyte or megabye of data is charge.

Figure 1: Wireless Data Cost

Wireless messaging is a teleservice as it processes the user data. Wireless messaging services include store, forward, and Internet connectivity. Typically wireless messaging is combined (bundled) with wireless data service (such as packet data).

Broadcast Television

Broadcast television revenues are primarily obtained from the providing of advertising. Figure 2 shows the recent growth of the broadcast television advertising industry. This diagram shows that total advertising revenue is increasing.

Figure 2: Television Advertising Revenue.
Source: Television Advertising Bureau

Mobile Voice & Paging | Services

Mobile Voice

The most well known application for wireless communications is voice communications. Voice communication can be telephony; wide area (cellular), business location (wireless office) or home cordless (residential) or voice paging, dispatch (fleet coordination) or group voice (audio broadcasting). Service rates for voice applications typically involve an initial connection charge, basic monthly minimum fee, plus an airtime usage charge. When the customer uses service in another system than their home registered system, there may be a daily fee and/or a higher per minute usage fee.

Figure 1 shows that mobile telephone charges include recurring costs and usage costs. Mobile telephone systems also offer advanced features. In many cases, the advanced features are offered for free (e.g., voice mail) as they increase usage costs.

Figure 1: Mobile Telephone Costs

Paging

Paging services include tone paging, numeric paging, alpha (text) paging, and voice paging. Tone paging service notifies a paging customer that a message has been sent via a tone. This tone usually is designated to mean a callback to a single location is requested. The original “beep, beep” tone pagers that started it all have become very popular as entry-level private communications systems, including restaurants (beeping servers when orders are ready) and in other centralized locations where a tone page necessitates a choice in response to only one.

While the popularity of these types of pagers has decreased overall, some retailers continue to offer tone pagers as “loss leaders” allowing the publication of low prices in print ads to attract attention. Still, for dispatch operators or other industries that only need a response to a central office, tone pagers offer a cost-effective solution.

Numeric paging is the sending of paging messages, typically telephone numbers that are displayed on a small paging device. After the message is received, the user calls back the displayed telephone number to talk to the sender.

Figure 2 shows that the typical cost for numeric paging service typically involves signing up for local, regional, or nationwide coverage. Rate plans start with a monthly service charge that allows pages using a local telephone number. Additional charges may be assessed for 800 toll free and 0800 freephone access numbers. Paging carriers usually offer a maximum number of pages per month and pages that additional per-page charges may apply for pages that are sent beyond the pre-defined limit.

Figure 2: Paging Cost

Alpha paging displays numerical and textual information. This can take many forms, from verbatim text messages to weather reports. Messages can be recorded into voice mail where operators type them up and send them out, or callers can dictate messages to live operators directly. Many carriers bundle free news, weather and sports feeds from other sources. While some carriers offer unlimited numeric usage, many charge for additional pages (both numeric and text message) beyond a pre-defined limit. Some carriers charge so much per character while others simply charge by the message.

Voice pagers broadcast messages through a built-in speaker in the paging unit. Message volume settings can usually be set to loud, soft or private, through an earpiece.

Two-way pagers allow fully interactive capabilities, permitting users to respond to pages by sending an original or canned alphanumeric message. Additional hardware must be purchased (or leased). Customers can lease the paging device for about $15 per month or purchase it for around $399.00.

Wireless Local Loop (WLL)

Wireless local loop (WLL) service refers to the distribution of telephone service from the nearest telephone central office to individual customers via a wireless link. In some cases, it is referred to as “the last mile” in a telephone network. This term is a bit misleading, though, because the coverage area of a WLL system may extend many miles from the central office.

Competitive local exchange carriers (CLEC) are competitors to the incumbent local exchange carriers (ILECS) and are likely to use WLL systems to rapidly deploy competing systems. If CLECs do not use wireless systems, they must either pay the existing phone company for access to the local loop (resale) or dig and install their own wire to the local customers. Many countries, that do not have large wired networks such as the United States, are using wireless local loop as their primary phone system.

Figure 1 shows a wireless local loop system. In this diagram, a central office switch is connected via a fiberoptic cable to radio transmitters located in a residential neighborhoods. Each house that desires to have dial tone service from the WLL service provider has a radio receiver mounted outside with a dial tone converter box. The dial tone converter box changes the radio signal into the dial tone that can be used in standard telephone devices such as answering machines and fax machines. It is also possible for the customer to have one or more wireless (cordless) telephones to use in the house and to use around the residential area where the WLL transmitters are located.

Figure 1: Wireless Local Loop

The most basic service offered by wireless local loop (WLL) system is to provide standard dial tone service known as plain old telephone service (POTS). In addition to the basic services, WLL systems typically offer advanced features such as high-speed data, residential area cordless service, and in some cases, video services. To add value to WLL systems, WLL service providers will likely integrate and bundle standard phone service with other services such as cellular, paging, high speed Internet, or cable service.

WLL systems can provide for single or multiple-line units that connect to one or more standard telephones. The telephone interface devices may include battery back up for use during power outages. Most wireless local loop (WLL) systems provide for both voice and data services. The available data rates for WLL systems vary from 9.6 kbps to over several hundred kbps. WLL systems can be provided on cellular and PCS, private mobile radio, unlicensed cordless, and proprietary wideband systems that operate the 3.4 GHz range.

Wireless Cable (Wireless Networks)

Wireless Cable
Wireless Cable is the common term assigned to a radio frequency-based alternative to the cable TV distribution system. An example of wireless cable technologies is multichannel multipoint distribution system (MMDS) or local multichannel distribution system (LMDS). By 1998, there were over 10 million wireless customers throughout the world and over 1.1 million in the United States.

Wireless cable system can simultaneously supply local television channels and high-speed data services. MMDS has a high-speed standardized air interface allowing mass deployment of cable television service by the new unregulated telephone companies. Cable television providers, who have access to most homes, can now provide telephone service.

In 1996, some analog MMDS systems began upgrading to digital service. Through the use of digital video compression, digital transmission allows 5 or 6 times the video channel capacity. In addition to video programming, wireless cable can provide telephone service and data services.

Figure 1 shows that the major component of a wireless cable system is the head-end equipment. The head-end equipment is equivalent to a telephone central office. The head-end building has a satellite connection for cable channels and video players for video on demand. The head-end is linked to base stations (BS) which transmit radio frequency signals for reception. An antenna and receiver in the home converts the microwave radio signals into the standard television channels for use in the home. Like traditional cable systems a set-top box decodes the signal for input to the television. Low frequency wireless cable systems can reach up to approximately 70 miles.


Figure 1: Wireless Cable System
Wireless cable is one of the most economical technologies available for the delivery of pay television service. Wireless cable systems do not require extensive networks of cables and amplifiers, bringing the offered price generally lower than a traditional cable service. To the customer, a wireless cable system operates in the same manner as a traditional cable system. Because wireless signals are transmitted over the air rather than through underground or above-ground cable networks, wireless systems may be less susceptible to outages, offer better signal quality and be less expensive to operate and maintain than traditional cable systems. In conventional coaxial cable distribution networks, the television signal quality declines in strength as it travels along the cables and must be boosted by amplifiers thus introducing distortion into the television signal.

To add security for wireless cable systems, so unauthorized users do not gain access to the system (stealing service), signals from video sources are scrambled with a code. The user must have the code to successfully view the video signals. Like traditional cable systems, wireless cable systems employ “addressable” subscriber authorization technology, which enables the system operator to control centrally the programming available to each individual subscriber, such as a pay-per-view selection

There are two primary methods of providing a communication path back from the end customer to the network operator: a telephone line and wireless. Wireless cable systems have typically only provided wireless downlink service (radio transmission from the system to the customer). Some of the new wireless cable systems now dedicate some of their radio channel capacity to uplink channels (from the customer to the system). Uplink channels allow the customer to select programming sources (such as pay per view) or may allow two-way Internet access.

Wireless Piconets (Wireless Networks)

Wireless Piconets
Wireless piconets are very small networks that connect 5 to 10 devices or allow access to each other. Wireless piconets are primarily personal networks that allow accessories such as printers and headsets and other devices to interconnect without the need for wires. These communication systems allow for the connections to be dynamically added and removed between devices.

A particular form of wireless piconet is called Bluetooth. The Bluetooth system is an industry standard wireless data network. Information and the specifications for Bluetooth can be found at www.Bluetooth.com.

Figure 1 shows Bluetooth devices that have created temporary connections. In this diagram, the personal digital assistant (PDA) device is synchronizing (deleting, changing, and adding) addresses with a laptop computer. The laptop computer is also connected to the Internet through a Bluetooth enabled access node. A mobile phone is also synchronizing its phone book listing with the laptop computer. However, because it is out of direct range of communicating with the laptop, it communicates through the access node. The mobile phone is also communicating with a wireless headset.


Figure 1: Bluetooth Wireless Piconet

Residential Cordless (Wireless Networks)

Residential Cordless
Cordless systems are short-range wireless telephone systems that are primarily used in residential applications. Cordless telephones regularly use radio transmitters that have a maximum power level below 10 milliWatts (0.01 Watts). This limits their usable range to 100 meters or less.

The earliest generation of home cordless telephones used a single radio channel that used amplitude modulation. These first generation cordless phones were susceptible to electrical noise (static) from various types of electronic equipment such as florescent lights. The noise encountered when using these phones sometimes created a consumer impression that cordless telephone quality was below standard wired telephone quality. Improved versions of cordless phones that used FM modulation to overcome the electrical noise resulted. As cordless phones became more popular, interference from nearby phones became a problem. In apartment buildings where there were many users of cordless phones in close proximity, the ability to initiate and receive calls could be difficult as radio channels became busy with many users. This led to the development of cordless phones that used multiple radio channels. As voice privacy became more of an issue, cordless phones began to use scrambled voice. Some of these voice privacy systems were analog while a majority of cordless phones that offer voice privacy use digital transmission.

Figure 1 shows the evolution of cordless telephones. Until the mid 1990’s, most cordless telephones were limited to use in a small radio coverage area of their base station that was usually located in the home. That home base station was normally connected to the telephone line of the owner (either residential or a single office telephone line) and they were not intended to serve the general public. To add more value to the use of cordless phones, cordless telephones evolved to allow access to base stations in public locations. Cordless telephones could then be used in the home and in areas that were served by public base stations. The next evolution for cordless telephones was the combination of other types of wireless products and services into the cordless phone. This included the combination of wireless office and cellular telephones into a cordless phone.


Figure 1: Evolution of Cordless Telephone Systems
Most home cordless telephones used frequencies in unlicensed radio frequency bands. Because so many homes operate cordless phones, each manufacturer must build-in circuitry to minimize the interference caused by other cordless devices. The original cordless phones use a very crowded frequency band (around 27 and 49 MHz) utilizing analog radio wave modulation. Recently, cordless telephones have been developed that operate in the 902-928 MHz unlicensed industrial, scientific, and medical (ISM) frequency band.

Residential cordless telephones must automatically coordinate their radio channel access as they operate independently of any type of network control. To coordinate radio channel access and avoid interference to other cordless handsets installed in the vicinity, cordless phones perform radio channel scanning and interference detecting prior to transmitting a signal.

Because cordless telephone systems do not as a rule have a dedicated control channel to provide information, the cordless handset and base station continuously scan all of the available channels (typically 10 to 25 channels). Figure 2 shows the basic cordless telephone coordination process. This diagram shows that when the cordless phone or base station desires to transmit, the unit will choose an unused radio channel and begin to transmit a pilot tone or digital code with a unique identification code to indicate a request for service. The other cordless device (base station or cordless phone) will detect this request for service when it is scanning and its receiver will stop scanning and transmit an acknowledgement to the request for service. After both devices have communicated, conversation can begin. When another nearby base station detects the request for service, it will determine that the message is not intended for it and will not process the call and scanning will continue.


Figure 2: Cordless Telephone System