Third Generation Communication Systems: Future Developments and Advanced Topics

The evolution from 1G to 5G is summarized in Table 1. Existing base station designs must service different bands with different cell sites, where each site has multiple base stations one for each frequency or technology usage e. To procure new spectrum, it can take a decade of legal formalities through the regulatory bodies such as International Telecommunication Union ITU and U. When spectrum is finally licensed, incumbent users must be moved off the spectrum, causing further delays and increasing costs.

Based on the Internet Protocol Architecture of 4G communication systems, unprecedented numbers of smart and heterogeneous wireless devices will be accessing future 5G mobile and wireless communication systems with a continuing growth of Internet traffic. Moreover, energy efficient concepts will be fully integrated into future wireless communication systems to protect the environment. To meet the above challenges, 5G mobile and wireless communication systems will require a mix of new system concepts to boost spectral efficiency, energy efficiency and the network design, such as massive MIMO technologies, green communications, cooperative communications and heterogeneous wireless networks.

We expect to explore the prospects and challenges of 5G mobile and wireless communication systems combining all of the above new designs and technologies. Thus concluding, simultaneous management of multiple technologies in the same band limited spectrum is a challenge in 5G mobile communication which supports going beyond voice for newer smart phones and advanced mobile devices. Gathered data for meeting the requirements and satisfactory constraints are highly valuable for the development of 5G cellular communications at mm bands in the coming decade. The present weather radar users—e.

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These arguments can most readily be based on the ability of the longer-wavelength S-band radar systems to penetrate heavy precipitation and allow the proper interpretation of hydrometeor scattering without the complications that arise when the hydrometeor sizes are large relative to the radar wavelength. Policy makers and members of the operational community should actively participate in the arena of frequency allocation negotiation. The impact, including the economic and societal costs, of restrictions on operating frequency, bandwidth, and power should be assessed for current and future weather radar systems.

Collecting and processing base data the radar reflectivity, the radial velocity, and the spectrum width parameters and the derived diagnostic meteorological products provide the bulk of the operational experience with NEXRAD. These experiences reveal data-quality problems. These problems are being addressed in open-systems architecture activities. The problems should continue to be addressed in the future system. Data corruption usually results from such factors as range folding, normal and anomalous propagation ground clutter, velocity aliasing, radio frequency RF interference, improper maintenance procedures, and nonatmospheric reflectors such as birds or chaff.

Depending on the situation, the impact of these artifacts on generating an accurate meteorological product varies between minimal and severe. Product degradation can take the form of an enlarged data void when contaminated data are detected and censored, or it can take the form of erroneous products when biased data are passed on to meteorological algorithms. Experience has shown that the integration of data-quality analysis prior to data assimilation is an effective way for detecting and masking erroneous data, thereby preventing the introduction of faulty information into the product algorithms.

An automated data-quality analysis system should be an integral component of the next generation radar system. The primary component should be automatic detection of known artifacts and flagging of that data for special treatment prior to generation of any products using the radar base data.

Certainly, these data-quality issues must be addressed within the data assimilation scheme if not sooner. Even more important for proper data assimilation is the knowledge of error statistics of each data source. Not only must the instrumentation error be known, but also the representativeness error of the specific measurements must be estimated for effective assimilation by a numerical model. The quality of real-time data should receive prominent consideration in the design and development of a next generation weather surveillance radar system.

Although several studies are underway to address these important data-quality issues, two technological developments can provide a major improvement—polarimetric observations and electronic, agile beam scanning. Tests on polarimetric radar tests are already being performed as part of a potential WSRD upgrade in the next decade.

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Polarization diversity observations bring some unique characteristics that are important for addressing data-quality issues. First, without any additional effort, polarimetric measurements automatically suppress the second trip echoes by about 15—20 dB depending on the type of hydrometeors.

Third, the differential polarization parameters, such as differential reflectivity and specific differential propagation phase, are immune to absolute calibration errors. Furthermore, self-consistency constraints of the covariance matrix measurements in rain impose bounds on errors in absolute reflectivity measurement Scarchilli et al. Dual-polarized radar systems can be configured in different ways depending on the measurement goals and choice of orthogonal polarization states.

Fully polarimetric radar measures the complete covariance matrix of precipitation in the resolution volume Bringi and Chandrasekar, Radars can be operated with polarization agility where the transmit polarization is changed on a pulse-to-pulse basis and two orthogonal polarizations are received, providing polarization diversity on reception.

Alternatively, radars can transmit and receive the same polarization states, or utilize a hybrid mode in which they are different. The hybrid mode of operation where both horizontal and vertical polarization states are simultaneously transmitted but separately received is the mode being considered for the current WSRD upgrade. The deficiencies have been identified as a limiting factor for the value of the NEXRAD system in support of hydrologic products, including. It is anticipated that the addition of a polarimetric capability to the NEXRAD will address, in part, these limitations.

Dual-polarization measurements allow improved accuracy in the rainfall determination, more effective hail detection, and an effective means for characterizing hydrometeors throughout a storm volume. The improved accuracy in the determination of rainfall arises from the inclusion of differential reflectivity Z dr , which is an effective estimator of drop size, and specific differential phase shift K dp as additional radar parameters to supplement reflectivity factor Seliga and Bringi, , ; Sachidananda and Zrnic, ; Bringi and Chandrasekar, The polarimetric radar will also permit the development of precipitation particle type products, an important addition to the diagnostic product suite Vivekanandan et al.

Plate 1 shows an example of vertical sections of reflectivity and hydrometeor type obtained from polarimetric radar. Independent of the impact on precipitation estimates, polarization diversity capability will contribute significantly to improving data quality Chandrasekar et al. The next generation radar system should preserve the polarimetric capability anticipated for the WSRD, and special attention should be given to the development of products to quantify precipitation rate and to determine precipitation type.

The present inability of the WSRD to identify the bright band, and the inadvertent introduction of bright-band reflectivity bias into precipitation and storm products, has been identified as a recurring data-quality problem in existing NEXRAD products. The introduction of a polarimetric capability will allow for the development of high-quality bright-band information that can be used to compensate biased rainfall estimates. Polarimetric measurements offer a significant contribution to improved radar data quality, and the polarimetric capability is important to preserve within the framework of future radar systems.

Other new capabilities of future radar will likely include much faster volume scans, or Volume Control Pattern VCP updates. Data quality can be improved using the precise steering of phased arrays to minimize clutter echoes. Rapid beam steering combined with flexible waveforms will offer new opportunities to minimize second trip echoes and to prevent velocity aliasing.

However, these new digital processing and data storage requirements are not likely to limit the performance of the sensor systems described here. In addition, increased use of optical and wireless communications between the individual sensors and networks is envisioned. Advanced radar technology can reduce, but not completely eliminate, data corruption due to ground clutter. Electronically scanned phased array radar has the flexibility to suppress ground clutter entering the main beam by steering the main beam immediately above clutter objects appearing on the horizon moun-.

Further, electronic scanning allows complete removal of beam spreading and degradation caused by beam motion during the data acquisition interval, thereby yielding improved clutter rejection of both normal and anomalous propagation-induced clutter.

Third Generation Communication Systems: Future Developments and Advanced Topics

The inherent beam agility allows rapid steering in other directions when objectionable interference beyond the primary echo is being received. Adding a second wavelength sensing capability would likely raise the cost to several hundred dollars per module. An alternative architecture utilizing a rotating single array appears entirely satisfactory for the next generation weather radar.

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A simple rotating slotted waveguide array has been proposed for a one-dimensional elevation steering concept of a single agile beam Smith, ; Keeler and Frush, ; Josefsson, ; Holloway and Keeler, In its simplest incarnation, the rotating array covers the azimuth region by slow mechanical scanning while the elevation region is covered by an array tilted back about 20 degrees and using standard rapid 1D electronic scan steering techniques.

Plate 2 shows a conceptual schematic of such a system.

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As the first wave of third-generation communication devices arrives, the technological and societal effects are Future Developments and Advanced Topics. Third Generation Communication Systems: Future Developments and Advanced Topics: Jian-Guo Ma.

The single beam may be rapidly scanned electronically in elevation using frequency or phase steering that requires on the order of only phase shifters instead of several thousand. In combination with a high-resolution pulse waveform, range averaging of independent high-resolution samples permits accurate base data estimates in a short dwell time. In this manner, a large volume can be scanned in time intervals on the order of a minute with spatial resolution. This approach requires increasing the transmit bandwidth, which will likely be complicated by future spectrum allocation issues.

Typically, the phased array can electronically scan up to 20 degrees off a direction normal to the antenna plane without severely altering the beam shape. It may be advantageous to execute a second mechanical sweep with the antenna tilted to a higher elevation and accept a corresponding loss in VCP update rate.

A somewhat more complex and costly architecture utilizing 1D scanning in elevation but, in addition, having limited azimuth scan-back capability may be required for certain near-surface measurement applications requiring long dwell times, such as ground clutter cancellation or clear air detection of weak atmospheric signatures. Another architecture uses a small phased array feed, possibly only a linear array that illuminates a reflector that forms the main beam or beams.


Digital beam forming DBF is feasible with some types of array feed systems, but beam shaping and sidelobe control may be difficult. Multiple-beam phased array systems have been proposed Skolnik, ; Hansen For example, multiple transmit beams, each having relatively high sidelobes using a high-power transmit antenna, could be coupled with a precision, low-power receive phased array capable of high overall isolation between the individual beams.

Frequency steering techniques or digital beam forming technology would allow the same rapid VCP coverage while using longer dwell times on each beam. The primary disadvantage of multiple-beam architectures is the increased design effort necessary to assure high isolation between the simultaneous beams. Furthermore, the transmitter must generate a correspondingly higher average power and a greater number of multifrequency waveforms in the frequency steered case to maintain sensitivity.

The same trade-off applies for single-beam techniques using pulse compression—the average transmit power must be increased to maintain sensitivity for a given range resolution.

Design tradeoffs in these alternative architectures are somewhat different. In the pulse compression single-beam system, the range sidelobes of the compressed waveform should be minimized to maintain the contrast in strong radial reflectivity gradients. In digital beam forming and frequency steered multiple-beam configurations using simultaneous transmit beams, advanced receiver beam shape design is needed to maintain isolation of nearby beams.

Precision beam shaping may be achievable using low-power pin-diode phase shifters that are not required to accommodate the high-power transmit pulse. Phased array architectures may be based on different array technologies. Active antenna technology has not been cost effective in the past, but future monolithic microwave integrated circuit MMIC designs and high volume may allow economical production for the next weather radar system.

This antenna will be coupled with a WSRD transmitter, a modern digital receiver and signal processing system, and eventually a pulse compression waveform. This phased array test bed, cumbersome by present standards, will be operated to test and evaluate phased array scanning techniques that will likely employ modern, cost-effective array technologies for a future implementation. Slotted waveguide antenna technology offers a viable technology for phased array radar steerable in one dimension. When coupled with a high-range resolution waveform, these systems allow much faster volume update rates.

Furthermore, antenna beam forming has analogies in spectrum analysis that may provide new insights for high-resolution antenna beams Palmer et al. The likely need to have polarization diversity integrated with the phased array places special constraints. TASS studies Rogers et al. Studies at Ericsson Josefsson, have shown that a slotted ridge waveguide can generate dual-polarization beams.

However, these same studies indicate that the polarization becomes distorted when beams are steered away from the principal axes only in azimuth or elevation from bore sight. Compensation may be possible since these are fixed, predictable patterns. The data-quality benefit will be attained even if the polarization purity deteriorates slightly in phased array antenna implementations when the beam departs from bore sight. These effects must be carefully considered in the design of any new radar system.

Because technology continues to evolve, it is important that there be further investigation and analysis of the risks, costs, and benefits that drive an advanced radar architecture decision. This analysis could lead to a conclusion that the costs and risks of the phased array technology are acceptable for the next generation system. In that event, research will be needed into the development of the appropriate prototype radar technology and processing algorithms for phased array systems.

This research is necessary risk mitigation, so that appropriate information is available concerning options and benefits of a network of phased array radars and associated sensors. The technical characteristics, design, and costs of phased array radar systems that would provide the needed rapid scanning, while preserving important capabilities such as polarization diversity, should be established. The volume update rate is a critical factor limiting the effectiveness of many meteorological products.

Pulse compression utilizes a long, low peak power waveform coded in phase, frequency, or amplitude to effectively compress the full energy of the extended pulse to a much shorter resolution interval. Pulse compression techniques or short, high peak power pulses may be employed to acquire independent samples in range that may be averaged to obtain statistically accurate information in a short dwell time.

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For many aviation and military applications, an extended waveform using a form of pulse compression is entirely acceptable. However, for distributed weather scatterers, the integrated sidelobe contamination presents a large obstacle in the strong reflectivity gradients characteristic of convective weather.

Various waveform designs have been proposed to reduce this contamination using nonlinear FM and other techniques of pulse shaping to reduce the Doppler sensitivity of the compression technique Keeler and Hwang, ; Mudukutore et al. As other techniques of obtaining independent samples to reduce volume updates times are developed, these obstacles will be overcome.

The wind profiler processing technique of range imaging Palmer et al. Inverse whitening filter processing techniques to increase the number of independent range samples Keeler and Griffiths, ; Torres and Zrnic, may also find application to radar waveforms. In contrast to the distributed transmitters and receivers characteristic of active array technology, present microwave radars use klystrons, magnetrons, and. Much has been written on solid-state transmitters regarding reliability and waveform flexibility. Even high average power solid-state transmitters are known to have high reliability and extremely low phase noise characteristics, primarily because they operate from low-voltage power supplies.

They may be designed with failure-tolerant modes so that an entire second back-up transmitter is not required in operational systems as is the case for transmitters based on klystrons and traveling wave tubes TWTs. However, solid-state transmitters lack the high peak power pulsing capability that may ultimately be required of a new generation weather radar system. Pulse compression of long, low peak power waveforms is a natural resolution; however, range sidelobe contamination in high-reflectivity gradients may limit the quality of the measurements. A definitive feasibility demonstration is needed for pulse compression techniques for weather radars before low peak power solid-state transmitters can be seriously considered for the next generation radars.

A second shorter wavelength combined with an S-band system has been implemented within the research community for attenuation-based rainfall estimation and Mie scattering-based hail detection.

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The European community dropped this option after the COST study cited potential practical problems, the major one being beam matching Meischner, However, this technology is the one that is planned for the next space-borne radar system to be carried on the Global Precipitation Mission GPM. In view of these conflicting pursuits, it is not clear whether dual-wavelength radar offers any additional benefit for future advanced weather radar.

Phased array radars offer another advantage over standard prime-focus reflector antenna systems. By separating the full array into two possibly overlapping subarrays in the receive mode and simultaneously processing the two beams, it is possible to retrieve the tangential wind component in the direction connecting the center of the two subarrays.