- Digital RF Transport. - The Advantage of Digital RF Transport for Distributing Wireless Coverage and Capacity. - Used for both indoor and outdoor, low power and high power applications, RF transport solutions link remote antennas and cell sites to base transceiver stations.. - Analog and digital RF transport systems feature significant differences that impact network performance. - Analog RF transport systems may transport digitally modulated signals, such as TDMA or CDMA. - Or analog RF transport systems may include a data path for carrying alarm information. - Also, the network components required to support analog RF transport—including lasers, splitters/combiners, converters, and repeaters—are all analog devices.. - Unlike analog RF transport systems, digital RF transport solutions involve digitization of RF signals. - With 14 bit samples taken at 71 Mbps, the resulting digitized representation of the RF signal is over 1 Gbps with dynamic range performance that can practically exceed 70 dB over all conditions.. - The relationship between dynamic range, loss, and noise in RF transport. - Dynamic range is like bandwidth—more is better.. - Expressed in decibels (dB), dynamic range is the difference between the strongest signal and signal just above the noise floor.. - Comparing the dynamic range of analog and digital RF transport systems is like comparing the dynamic range of. - The dynamic range of a LP record is about 50 dB. - For a compact disc, dynamic range is about 90 dB. - In wireless communications, poor dynamic range is most apparent in data communications. - Clearly, wide dynamic range is critical as more data services consume the wireless spectrum.. - What limits dynamic range in an analog RF transport system? Loss and noise. - And RF transport systems generate a variety of noises. - Figure 2 compares the impact of loss and noise in analog and digital RF transport systems.. - It is loss and noise that make digital and analog RF transport systems so different. - In all analog RF transport systems, loss and noise generated in the transport are directly added to the RF signal. - Source of Loss of Dynamic Range in Loss of Dynamic Range in Loss/Noise Analog RF Transport Systems Digital RF Transport Systems. - Comparing loss of dynamic range in analog and digital RF transport systems. - Unlike analog systems, noise and loss have virtually no impact on digital RF transport because the discrete values of the digitized RF signal and the transport medium are fully independent. - In digital RF transport over fiber, as long as the digital bit stream is transported over allowed optical transport requirements—. - With digital RF transport, as long as the signal can be detected, the digitized RF signal is transported error free, as depicted in Figure 3.. - Before transmission over an RF transport system, the dynamic range of the signal is therefore 70 dB. - In a digital transport system over fiber cable, the dynamic range of the digitally transported RF signal remains constant at 70 dB—irrespective of optical loss and noise generated in transport. - By contrast, in an analog RF transport system—where losses and noise are permanently added to the RF signal—adding 25 dB of optical loss reduces dynamic range by 50 dB, resulting in a dynamic range of 30 dB. - Even as optical loss grows, digital RF transport maintains dynamic range of the signal.. - The cumulative effects of loss quickly degrade analog RF transport.. - Loss of dynamic range inhibits the information carrying and call handling capability of analog RF transport systems. - Digital RF transport systems—immune to degradation caused by noise in the transport that affects analog RF transport systems—offer a wider dynamic range and greater performance for wireless communications. - Greater dynamic range allows strong and weak signals to be transported simultaneously, which translates into improved quality of service.. - The relationship between noise, higher speeds, and signal strength in RF transport. - Because digital RF transport is immune to transport noise, a higher SNR is possible than with analog RF transport systems. - With a better SNR, digital RF transport delivers significantly better signal quality that translates into higher data rate capabilities.. - With an inherently higher SNR, digital RF transport maximizes use of valuable spectrum and offsets shrinking coverage areas caused by higher speed services. - Improved performance of digital RF transport on the reverse path enables higher power of the forward path, resulting in a balanced path, something sacred to network designers. - increased SNR—translate into wider dynamic range, both the more distant, weak signals and strong signals are detected on the return path of a digital RF transport system. - With higher forward path output and greater sensitivity to both weak and strong signals on the uplink, digital RF transport—with higher SNR and wider dynamic range—ensures enhanced coverage and a balanced path.. - Higher noise limits signal strength in analog RF transport.. - Because digital RF transport is immune to optical transport noise, greater signal quality is achieved—enabling higher data rates, better use of spectrum, and wider coverage areas on the forward and return paths. - With higher SNR, digital RF transport improves QoS by maximizing coverage and preserves capital by maximizing valuable spectrum and network equipment.. - The foolproof method for ridding an analog RF transport system of noise is to reduce cable distance. - For analog RF transport in coarse wave division multiplexing (CWDM) applications, fiber cable distance can be limited to only 2 to 4 miles, which may mean only a mile of straight line distance. - For distance, analog RF transport systems just can’t measure up to digital RF transport systems, effectively imposing limits on network design and system performance.. - Analog RF transport systems do have an array of methods to compensate for noise and increase distance. - Automatic Gain Control devices are essential for analog RF transport systems, even though there is a limit on the total number of loss/gain blocks in the system. - And even with these measures, noise from splitters, connectors, converters, cables and other sources still limit the performance of analog RF transport systems.. - With digital RF transport, distance is virtually unlimited. - Figure 5 shows how digital RF transport maintains dynamic range over greater distances.. - Digital RF transport maintains dynamic range over longer distances, allowing network planners more flexibility in design. - The distance limitations of analog RF transport systems are due to the basic weakness in all analog RF transport systems—the cumulative effects of noise and loss reduce dynamic range and signal strength.. - With 1.5 dB of optical loss per mile and 6 dB CWDM loss, digital transport of RF signals maintains dynamic range for over 12 miles.. - At this rate of optical loss, analog RF transport can only maintain dynamic range for less than 4 miles.. - Digital RF transport stands for flexibility. - The relative noise immunity of digital RF transport systems delivers wider dynamic range, higher SNR, increased signal output, and virtually unlimited distance—all of which translates into improved quality of service in terms of coverage, clarity, and speed. - Yet the key benefit of digital RF transport lies in a factor cherished by planners, engineers, operations personnel, and CFOs alike—. - ADC’s patented digital RF transport technology supports AMPS, TDMA, CDMA and GSM. - In addition, digital RF transport is not designed for any particular handset, any particular base transceiver station equipment, or any specific architecture.. - Digital RF transport works with singlemode fiber, multimode fiber, millimeter wave connections, and free space optics. - Choosing digital RF transport is truly a choice for today and the future.. - As wireless data rates increase and coverage areas shrink, digital RF transport offers greater flexibility. - particularly suited for the task because the digital RF signal and the optics are. - This is not true for analog RF transport systems where leakage from one channel to another degrades performance of the RF signal as well as signals in adjacent channels. - In fact, network planners will find that many CATV and metro area network rings are not set up to handle the effects of analog RF signal transport on the fiber plant.. - Digital RF transport offers improved flexibility in design for indoor applications, too. - “Home run” fiber cable runs are often required in analog RF transport systems, significantly increasing installation costs and inhibiting expansion capabilities. - Digital RF transport systems split and add signals digitally, so the architecture of fiber cable runs can be optimized for each application, minimizing installation costs and time.. - Improved QoS from digital RF transport reduces churn. - And most importantly, digital RF transport significantly reduces capex and opex when deploying networks with centralized radio capacity through base station hotels. - Digital RF transport gives an edge to a wireless service provider to compete today and tomorrow.. - 2 Blocking Dynamic Range (BDR) is the difference between the noise floor and the 1 dB compression point. - Example: if a system has a 10 dB noise figure (a 30 kHz noise floor of -119 dBm) and a level limiting threshold 0f -40 dBm (which compresses gain by 1 dB at -39 dBm), then the blocking dynamic range would be dB. - Dynamic Range of RF Transport Systems. - Digital RF transport systems are immune to the noise and loss that degrades the performance of analog transport systems. - In the above example, the shaded area shows that acceptable system operation requires dynamic range between 60 dB and 80 dB. - The analog RF transport system starts off strong with a dynamic range of 80 dB.. - However, as the analog RF signal traverses. - various cables, modules, patch cords, and splices, noise and loss quickly degrade dynamic range to less than 40 dB. - On the other hand, digital RF transport maintains dynamic range of 70 dB all the way from remote antenna to the base transceiver station.. - Appendix A – Comparing Dynamic Range of RF Transport Systems. - Analog RF transport
Xem thử không khả dụng, vui lòng xem tại trang nguồn hoặc xem
Tóm tắt