Presented by:
K.Bhagyasree
M.Ramyasudha

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INTELLICELL
A FULLY ADAPTIVE APPROACH TO SMART ANTENNAS
ABSTRACT
Cellular communications has reached mass-market status over the past decade with the emergence of two very successful standards: CDMA and GSM. Over this same decade, an important enabling technology, “smart antennas,” has also matured. Combined with today’s powerful, low-cost processors, advanced smart antenna technology is destined to become an important part of the cellular landscape over the next decade.
IntelliCell is the name for these developing smart antenna techniques and intellectual property for commercial cellular systems. Through eight years of practical and field implementation, IntelliCell has been perfected to make smart antennas practical and cost effective in actual commercial cellular systems. Today, IntelliCell technology is deployed in more than 90,000 commercial base station deployments worldwide.
Finally, though this paper has focused on IntelliCell implementations at the base station, the technology is equally applicable to handsets and subscriber units. Today’s trends in handset component costs and processing capabilities point to this being the next major frontier for IntelliCell and smart antenna technologies.
1.Introduction:
Smart antenna systems utilize multiple antennas at base stations or handsets to better pinpoint or focus radio energy and thereby improve signal quality. Since cellular communications systems employ radio signals that interact with the environment and each other, these improvements in signal quality lead to system-wide benefits with respect to coverage, service quality and, ultimately, the economics of cellular service. To some extent, the phrase “smart antennas” is misleading. There is nothing smart about the antennas themselves. What’s smart is the sophisticated signal processing applied to simultaneous signals from an array or collection of multiple antennas.
Basic Cellular Architecture:
Cellular networks are composed of geographically separated base stations connected to a backbone network, with each base station serving an area called a cell. (See Figure 1.) In some systems, cells are further subdivided into sectors, for reasons that will be described later in this document. Handsets communicate with a nearby base station via radio signals. The information, voice or data, is digitized prior to transmission in all modern cellular systems. End-to-end connections with public or private data or telephony networks are made possible by a backhaul network that connects all of the base stations to a switching/routing function, which directs users’ voice or data transmissions to and from their correspondents.
In the radio portion of the network, the “uplink” refers to the communication from the handset “up to” the base station. The handset or user terminal suitably digitizes and frames voice or packet data meant for the network. This digitized data then is modulated using digital and radio circuitry and transmitted via the antenna in the handset. The antennas and circuitry at the base station receive the radio signal, demodulate it and send the user’s information on into the wired network.
The “downlink” refers to the reverse direction, where the communication is from the base station “down to” the handset or user terminal. The base station suitably digitizes and frames voice or packet data meant for the subscriber. This digitized data is modulated using digital and radio circuitry and is transmitted via the antennas at the base station. The antenna and circuitry at the handset receive the radio signal, demodulate it and send the information on to the subscriber. This type of cellular architecture has gained wide acceptance as the most economical and flexible architecture for delivering mass-market personal wireless services.
2. Coverage:
The base station range (cell area) determines the number of base stations required for a particular coverage area in the early days of deployment, when subscriber density is low. It is, therefore, one of the key determinants of system economics. When radio energy propagates in a cellular environment, the received signal level degrades as the distance between transmitter and receiver increases. This received signal has to exceed the inherent noise level in the radio receiver by a certain margin in order to be successfullydemodulated.
Everything else being equal, a higher nominal SNR translates into a higher possible data rate but at the cost of reduced base station range. Some systems operate at much lower SNRs by introducing large redundancy into transmitted data through a process known as “spreading.”
3.Spectral Efficiency:
Besides coverage, next-generation cellular systems face another challenge related to “spectral efficiency.” Spectral efficiency measures the ability of a wireless system to deliver information with a given amount of radio spectrum and is directly related to

system capacity. It determines the amount of radio spectrum required to provide a given service (e.g., 10 kbps voice service, 100 kbps data service) and the number of base stations required to deliver that service to the end-users.
Spectral efficiency is measured in units of bits/second per Hertz/cell (b/s/Hz/cell). It determines the total throughput each base station (cell or sector) can support in a given amount of spectrum. The key benefits of higher spectral efficiencies can be enumerated as follows: higher aggregate capacity (per-cell throughput); higher per-user quality and service levels; higher subscriber density per base station; small spectrum requirements; and lower capital and operational costs in deployment. The spectral efficiency for various systems can be calculated easily via the formula:
Spectral Efficiency = (Channel Throughput/Channel Bandwidth)
This simply sums the throughput over a channel in an operating network and divides by the channel bandwidth. This calculation is performed for a number of systems in Table 1.
The value of approximately 0.1 b/s/Hz/cell is generally representative of high-mobility 2G and 3G cellular systems, including CDMA systems of all types. It reflects the fact that the classical techniques for increasing spectral efficiency have been exhausted and that new techniques are necessary. Finally, it should be noted that the value of 0.1 b/s/Hz/cell represents a major stumbling block for the delivery of next-generation services. Without substantial increases in spectral efficiency, 3G systems are bound to spectral efficiencies like those of today’s 2G systems. In a typical 3G system with a 5Mhz downlink channel block, this translates into a total cell capacity of approximately 500 kbps for the entire cell.
4. The Quest For Better Coverage And Spectral Efficiency:
A wide range of techniques and tradeoffs has been developed for enhancing coverage and spectral efficiency over the past 20 years. The most important and widely used are the following.
Frequency Planning: A substantial amount of the effort in cellular systems is devoted to managing interference through the use of a “reuse pattern.” Traffic channels are partitioned into groups.The resulting spatial separation ensures that the energy being used for a conversation in one cell has been sufficiently attenuated by the time it reaches another cell using the same channel that it does not pose significant interference. Reuse provides interference management, but at the expense of operational complexity and base station capacity..
Power control: Power control is a technique whereby the transmit power of a base station or handset is decreased to near the lowest allowable level that permits communication. This reduces interference levels in the network, increasing spectral efficiency.
Modulation and Coding:Modulation and coding techniques can improve the utilization of spectrum by allowing a faster throughput at a given signal quality. The benefits of any such techniques are ultimately limited, however, by the Shannon information rate.
Sectorization: Sectorized antenna systems take a traditional cell area and subdivide it into “sectors,” each covered by its own directional antenna sited at the base station location. Operationally, each sector is treated as an independent cell. Directional antennas have higher gain than omni-directional antennas, all other things being equal. Hence the range of these sectors is generally greater than that obtained with an omnidirectional antenna, roughly 35 percent greater. Sectorized cells can increase spectral efficiency by reducing the interference presented by the base station and its users to the rest of the network, and they are widely used for this purpose. Most systems in commercial service today employ three sectors per site. Although larger numbers of sectors are possible, the number of antennas and quantities of base station equipment become prohibitively expensive for most cell sites.
5. INTELLICELL: The Fully Adaptive Smart Antenna Approach:
Arrays of multiple antennas, combined with digital beam-forming techniques and advanced, low-cost signal processing open a new and promising area for enhancing wireless communication systems.
Terms commonly used to embrace various aspects of smart antenna system technology include intelligent antennas, phased arrays, spatial processing, digital beam forming, adaptive antenna systems, etc. IntelliCell is a battery of techniques and intellectual property that make smart antenna systems commercially viable.
A base station utilizing IntelliCell employs a small collection (array) of simple, off-the-shelf antennas (typically 4 to 12) coupled with sophisticated signal processing to manage the energy radiated and received by the base station. This improves coverage and signal quality and mitigates interference in the network on both the uplink and the downlink. The processes on the uplink and downlink are as follows:
5.1 The IntelliCell Uplink (reception at the base station)
Typically, the received signal from each of the spatially distributed antenna elements is multiplied by a weight, a complex adjustment of amplitude and phase. These signals are combined to yield the array output. An adaptive algorithm controls the weights according to predefined objectives such as “tuning in” to a particular user while “tuning out” interference and noise. This processing is performed independently and simultaneously for each of the users being served by the base station.These dynamic calculations enable the system to tune itself for optimized signal reception:The equivalent received signal level is improved by a factor of 10log10 (number of antennas),which, for example, is 10 dB for a 10-antenna system. At the same time, interference is rejected by many orders of magnitude, anywhere from 30 to 50 dB if an interfering signal is strong enough to warrant it. This rejection and the analogous suppression on the downlink are high enough that, in TDD/TDMA implementations of IntelliCell, frequency planning can be done away with completely. These gains and how they relate to overall gains in signal quality are summarized