Performance of autonomous dynamic channel assignment and powercontrol for TDMA/FDMA wireless access

We combine autonomous algorithms for dynamic channel assignment (DCA) and power control in a TDMA/FDMA wireless system as a medium access control (MAC) protocol. The DCA algorithm determines paired radio channels that experience the least interference and are least likely to cause interference. The power control algorithm uses local estimations of signal to interference ratio (SIR) at a receiver to iteratively command power adjustment on the desired transmitter. A common control frequency, which is frame-synchronized among base stations, provides all necessary information for DCA without blind slots. Computer simulations are used to evaluate system performance. Results from computer simulations demonstrate good spectrum efficiency and robustness. Although studied under a specific set of parameters, this type of MAC protocol can be applied in different wireless communications environments     

Spatial-temporal equalization for IS-136 TDMA systems with rapiddispersive fading and cochannel interference

In this paper, we investigate spatial-temporal equalization for IS-136 time-division multiple-access (TDMA) cellular/PCS systems to suppress intersymbol interference and cochannel interference and improve communication quality. This research emphasizes channels with large Doppler frequency (up to 184 Hz), delay dispersion under one symbol duration, and strong cochannel interference. We first present the structure of the optimum spatial-temporal decision-feedback equalizer (DFE) and linear equalizer and derive closed-form expressions for the equalizer parameters and mean-square error (MSE) for the case of known channel parameters. Since the channel can change within an IS-136 time slot, the spatial-temporal equalizer requires parameter tracking techniques. Therefore, we present three parameter tracking algorithms: the diagonal loading minimum MSE algorithm, which uses diagonal loading to improve tracking ability, the two-stage tracking algorithm, which uses diagonal loading in combination with a reduced complexity architecture, and the simplified two-stage tracking algorithm, which further reduces complexity to one M×M and one 3×3 matrix inversion for weight calculation with M antennas. For a four-antenna system, the simplified two-stage tracking algorithm can attain a 10^-2 bit error rate (BER) when the channel delay spread is half of the symbol duration and the signal-to-interference ratio (SIR) of the system is as low as 5 dB, making it a computationally feasible technique to enhance system performance for IS-136 TDMA systems     

Effect of dietary neutral detergent fiber concentration and forage source on performance of lactating cows

'Mott' dwarf elephantgrass, forage sorghum, 'Tifton 81' bermudagrass, and whole corn plant were stored as silage and fed as the only forage source in diets formulated to 31, 35, and 39% NDF. The 12 diets were fed for ad libitum intake as a TMR to midlactation Holstein cows, primarily to determine the effect of NDF concentration and forage source on DMI and milk production. Increased dietary NDF concentration linearly decreased DMI (3.69 to 3.35%) and OM intake (3.39 to 3.06%) as a percentage of BW and linearly increased NDF intake as a percentage of BW (1.15 to 1.32%). Production of milk (23.0 to 21.7 kg/d) and 4% FCM (20.7 to 19.6 kg/d) and percentage of milk protein (3.16 to 3.07%) decreased linearly as dietary NDF concentration increased. Cows fed dwarf elephantgrass silage or corn silage, which were higher quality forage sources based on greater rates and extents of fiber digestion, consumed more DM and produced more milk than cows fed sorghum silage or bermudagrass silage. Cows fed diets containing sorghum silage had the lowest DMI and milk production. Apparent digestibility of NDF and ADF from corn silage and dwarf elephantgrass silage was greater than that of sorghum silage and bermudagrass silage. In addition to dietary NDF concentration, digestibility of dietary fiber influences DMI and milk production.     

Soil carbon and nitrogen stocks in nitrogen-fertilized grass and legume-grass forage systems

Nutrient Cycling in Agroecosystems - Soils under grasslands contribute significantly to terrestrial carbon (C) and nitrogen (N) pools, and grassland management practices directly impact pool size...     

Spectrum resource allocation for wireless packet access withapplication to advanced cellular Internet service

The advanced cellular Internet service (ACIS) is targeted for applications such as Web browsing with a peak downlink transmission rate on the order of 1-2 Mbits/s using a wide-area cellular infrastructure. In order to provide bandwidth on demand using scarce radio spectrum, the medium-access control (MAC) protocol must: 1) handle dynamic and diverse traffic with high throughput, and 2) efficiently reuse limited spectrum with high peak rates and good quality. Most of the existing approaches do not sufficiently address the second aspect. This paper proposes a dynamic packet assignment (DPA) scheme which, without coordinating base stations, allocates spectrum on demand with no collisions and low interference to provide high downlink throughput. Interference sensing and priority ordering are employed to reduce interference probability. A staggered frame assignment schedule is also proposed to prevent adjacent base stations from allocating the same channel to multiple mobiles at the same time. Simulation results based on a packet data traffic model derived from wide-area network traffic statistics, which exhibit a “self-similar” property when aggregating multiple sources, confirm that this method is able to reuse spectrum efficiently in a large cellular system having many users with short active periods. Distributed iterative power control further enhances spectrum efficiency such that the same channel can be simultaneously reused in every base station     

Adaptive algorithms for reducing PCS network authentication traffic

Two authentication schemes (ASs) have been proposed in the Electronic Industry Association/Telecommunications Industry Association's (EIA/TIA) Telecommunications Systems Bulletins (TSBs) 51 for incorporation in the cellular industry Interim Standard IS 41 Revision C. In the first scheme, which we refer to as the WS scheme, a unique secret key [also known as shared secret data (SSD)] is shared only between the authentication center (AC) and handset. In the second scheme, referred to as the S scheme, the SSD is also shared with the visited system. The performance of the two schemes can be compared by using the expected number of call originations/terminations between two consecutive registrations or call-to-mobility ratio (CMR). Based on the message flow (accesses to databases), it is apparent that the S scheme outperforms the WS schemes if the CMR ratio is large. The CMRs of users will likely span a wide range and, even for the same user, will perhaps vary from time to time. It is therefore desirable to switch between the ASs based on the users' CMR to reduce the signaling network traffic. We propose two adaptive algorithms to determine how and when to switch between the ASs for a given user. Our performance study indicates that as the CMR of a user changes, the adaptive algorithms automatically select the best AS in real time     

On the capacity of cellular systems with MIMO

It is shown that the mutual information of a single, isolated, multiple transmit and receive antenna array link is maximized by transmitting the maximum number of independent data streams for a flat Rayleigh fading channel with independent fading coefficients for each path. However, if such links mutually interfere, in some cases the overall system mutual information can be increased by transmitting fewer streams     

Nutritive value, fermentation characteristics, and in situ disappearance kinetics of ensiled warm-season legumes and bahiagrass

This study determined the nutritive value, ensiling characteristics, and in situ disappearance kinetics of bahiagrass (Paspalum notatum Flügge ‘Tifton 9’), perennial peanut (Arachis glabrata Benth. ‘Florigraze’), annual peanut [Arachis hypogaea (L.) ‘FL MDR 98’], cowpea [Vigna unguiculata (L.) Walp. ‘Iron clay’], and pigeonpea [Cajanus cajan (L.) Millsp. ‘GA-2’]. All forages were harvested at maturity stages that optimized dry matter (DM) yield and nutritive value. After harvest, forages were wilted to 45% DM, and 4 replicate bales of each legume and 8 bales of bahiagrass were wrapped in polyethylene and ensiled for 180 d. After each bale was opened, the forage was thoroughly mixed, and representative subsamples were taken for laboratory analysis and in situ incubation. Wilting and ensiling decreased the rumen-undegradable protein, water-soluble carbohydrate, crude protein (CP), and in vitro true digestibility (IVTD) of bahiagrass, perennial peanut, and cowpea, and increased their neutral detergent fiber (NDF) concentrations. Among haylages, CP concentration was greatest for annual peanut, followed by perennial peanut and cowpea, and least for bahiagrass. In contrast, NDF concentration was greater in bahiagrass than in legumes. Pigeonpea had the greatest NDF concentration among legumes and lowest IVTD of all haylages. All haylages were aerobically stable for at least 84 h, but pH was lower in perennial peanut and cowpea than in pigeonpea. Ammonia-N concentrations tended to be greater in legume haylages than in bahiagrass haylage. Butyrate concentration was greater in annual and perennial peanut than in bahiagrass. Total VFA concentration was greater in annual and perennial peanut and cowpea haylages than in bahiagrass haylage. Undegradable DM fractions were greater and extent of DM degradation was lower in bahiagrass and pigeonpea than in other haylages but lag time and degradation rates did not differ. Annual and perennial peanut and cowpea haylages were as aerobically stable and had greater CP, IVTD, and extent of degradation than did bahiagrass haylage; therefore, they are promising forages for dairy cow diets in the southeastern United States.     

Adaptive antenna arrays for OFDM systems with cochannelinterference

Orthogonal frequency-division multiplexing (OFDM) is one of the promising techniques for future mobile wireless data systems. For OFDM systems with cochannel interference, adaptive antenna arrays can be used for interference suppression. This paper focuses on a key issue for adaptive antenna arrays, that is, parameter estimation for the minimum mean square error (MMSE) diversity combiner (DC). Using the instantaneous correlation estimation approach developed in the paper, an original parameter estimator for the MMSE-DC is derived. Based on the original estimator, we propose an enhanced parameter estimator. Extensive computer simulation demonstrates that the MMSE-DC using the proposed parameter estimators can effectively suppress both synchronous and asynchronous interference in OFDM systems for packet and continuous data transmission     

Transmitter diversity for OFDM systems and its impact on high-ratedata wireless networks

Transmitter diversity and down-link beamforming can be used in high-rate data wireless networks with orthogonal frequency division multiplexing (OFDM) for capacity improvement. We compare the performance of delay, permutation and space-time coding transmitter diversity for high-rate packet data wireless networks using OFDM modulation. For these systems, relatively high block error rates, such as 10%, are acceptable assuming the use of effective automatic retransmission request (ARQ). As an alternative, we also consider using the same number of transmitter antennas for down-link beamforming as we consider for transmitter diversity. The investigation indicates that delay transmitter diversity with quaternary phase-shift keying (QPSK) modulation and adaptive antenna arrays provides a good quality of service (QoS) with low retransmission probability, while space-time coding transmitter diversity provides high peak data rates. Down-link beamforming together with adaptive antenna arrays, however, provides a higher capacity than transmitter diversity for typical mobile environments