Over the past several years, wireless communications have seen dramatic advances in two distinct areas. On one hand, the demand for portable voiceband services has resulted in intense research efforts to improve performance and increase capacity through digital transmission. Such systems focus on wide-area narrowband communications, providing low-bandwidth network services to individual users in a portable fashion. On the other hand, the need for more flexible computer networks has led to the advent of wireless LANs such as the Motorola Altair. Such systems focus on local-area wideband communications, providing networking services to individual computers but usually they are not easily portable. However, the distinction between these two systems is rapidly blurring. As laptop computers place mobile computing resources in the hands of individuals, wireless technologies capable of providing wide-area, wideband services will clearly be needed. With this merging of computation and communications, individual users will have instantaneous and portable access to fixed information networks via a lightweight mobile unit. Furthermore, users will be capable of transferring data to other users and accessing fixed computing resources without any constraints on where or when such access takes place. As shown in the figure, the mobile unit will support a myriad of services, including full-motion digital video and high-quality audio data, and combine the functionality of today's analog mobile telephones, radio pagers, and laptop personal computers.
Analog and digital CMOS design for spread-spectrum wireless communications, Page 1 of 2
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