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

LAN Telephony

Local access network (LAN) telephony (sometimes called TeLANophy) use LAN systems to transport voice communications. LAN telephone technology is an evolution of voice over IP (VoIP) and the rapid acceptance of virtual private networks (VPN’s) as an alternative to leased line private networks. The ability to share data networks with voice systems offers significant cost reduction for telephone services.

Figure 1 shows a LAN telephony system. This diagram shows that a LAN telephone system consists of LAN telephones, a data network, a LAN call processing system, and a voice gateway to the PSTN. LAN telephones convert audio into digitized packets that are transferred on the LAN to the call processing computer (CTI system). Each LAN telephone has its own network data address. The call processing system communicates with LAN telephones over the same high-speed LAN data network that communicates with computers. When calls are received from the PSTN, the call processing system looks in the database to find the associated LAN telephone address (data address) and this address is used to alert the LAN telephone of an incoming call. When calls are originated from the LAN telephone, the dialed telephone number is passed to the call processing system. This system determines if the call is routed within the data network or if the voice gateway must be used to connect the call to the PSTN.


Figure 1: LAN Telephony

Future Enhancements: Packetized Voice, High-Speed Multimedia Services, Fiber Distribution Networks, Soft Switches

The future enhancements to public switched telephone networks include the conversion from circuit switched systems to packet networks, expanded fiber networks, multimedia services, and soft switching systems.

Packetized Voice
Packetized voice is the process of converting audio signals into digital packet format, transferring these packets through a packet network, reassembling these packets into their original data form, and then recreating the audio signals.

By the end of 2001, over 5% of international calls from the United States were over the Internet and more than 9.5% of all inter-exchange telecommunications calls were on managed packet switching networks [7]. Packetized voice transmission allows for key features such as dynamic bandwidth allocation and advanced services. To convert to packetized voice, the EO exchange is either replaced or supplemented by a packet switch.

Various protocols such as resource reservation protocol (RSVP) and real time protocol (RTP) have been developed to ensure the quality of service of voice packets that are transmitted through a packet network.

High-Speed Multimedia Services
High-speed multimedia services is the term used to describe the delivery of different types of information such as voice, data or video. Communication systems may separately or simultaneously transfer multimedia information. High-speed multimedia usually refers to image based media such as pictures, animation, or video clips. High-speed multimedia usually requires peak data transfer rates of 1 Mbps or more.

The providing (provisioning) of multimedia services requires communication lines that can have multiple channels and each of these channels may have different quality of service (QoS) levels. As a result, many emerging multimedia services are likely to use ATM.

Fiber Distribution Networks
Fiber distribution networks use optical fiber to distribute communication channels from the PSTN to end customers. There are three key distribution networks: fiber to the neighborhood (FTTN), fiber to the curb (FTTC), and fiber to the home (FTTH).

Figure 1 shows that public telephone networks have growth options. Initially, they are likely to install (FTTN) and use existing copper lines to reach the home. As demand grows for high-speed data communication services, additional fiber may be installed from the node to the curb (FTTC) to replace copper lines. Eventually, to achieve extremely high data rates to the home or business, FTTH or fiber to the basement (FTTB) may be installed.


Figure 1: Fiber Optic Networks

Soft Switches
Soft switches are interconnection switching systems that can dynamically change its connection data rates and protocols types by software control to provide for voice, data, and video services. Soft switches were developed to replace existing EO switches that have limited interconnection capabilities. Soft switches are packet based and can simulate multiple protocols such as Internet protocol and ATM. This allows for multiple types and simultaneous services to each customer with varying levels of QoS.