Charging analysis of GSAT-17 patch antenna
R. RenukaP.V.N. MurthyVaddi RaghavaiahP. SowjanyaVaria Ashok KumarS. Sravan KumarV. K. HariharanM. Nageswara Rao
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Abstract:
GSAT-17 spacecraft is one of the most complicated and technologically advanced Satellites being built by Indian Space Research Organisation (ISRO). The payload configuration of GSAT-17 spacecraft is 24 channels In Normal C-Band Transponders, 12 channels in Upper Ext. C-Band Transponders, 2 Channels in Lower Extended C transponders, 2 Channels each in MSS and DRT/SAR. For Lower Ext-C band, 0.75m × 0.77m Tx./Rx. patch array (8×4) antenna is designed for both uplink and downlink signals. This antenna is mounted on EV top of the satellite and provides coverage to southern Indian peninsula and Antarctica. This poses a charging threat, if not properly grounded, due to GEO spacecraft charging. Hence a good grounding scheme is necessary for ESD compliance. A study was taken up to assess the surface and internal charging effects on the antenna and proper grounding scheme was worked out to mitigate this problem.Keywords:
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Consider a single-user FDD system with multiple antennas at the BS and a single antenna at the user. We assume that the BS performs coherent transmission and reception in the downlink and uplink, respectively. To this end, downlink resources are employed to estimate the downlink channel at the user, while uplink resources are used to estimate the uplink channel at the BS and to relay a quantized version of the downlink channel estimate back to the BS. The transmit CSI for the downlink is estimated, quantized, outdated and affected by feedback errors, while the receive CSI for the uplink is just estimated. Besides the well-known tradeoff between the training and data payload in a one-way system, in a two-way system like a downlink/uplink FDD system, there is an additional tradeoff between both links due to the feedback. We consider the resource allocation of the downlink and uplink jointly taking into account the feedback and imperfect CSI. As a figure of merit we employ the sum of the downlink and uplink capacities.
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An uplink-downlink two-cell cellular network is studied in which the first base station (BS) with M 1 antennas receives independent messages from its N 1 serving users, while the second BS with M 2 antennas transmits independent messages to its N 2 serving users. That is, the first and second cells operate as uplink and downlink, respectively. Each user is assumed to have a single antenna. Under this uplink-downlink setting, the sum degrees of freedom (DoFs) is completely characterized as the minimum of (N 1 N 2 + min(M 1 , N 1 )(N 1 - N 2 ) + + min(M 2 , N 2 )(N 2 - N 1 ) + )/ max(N 1 , N 2 ), M 1 + N 2 , M 2 + N 1 , max(M 1 , M 2 ), and max(N 1 , N 2 ), where a + denotes max(0, a). The result demonstrates that, for a broad class of network configurations, operating one of the two cells as uplink and the other cell as downlink can strictly improve the sum DoF compared with the conventional uplink or downlink operation, in which both cells operate as either uplink or downlink. The DoF gain from such uplink-downlink operation is further shown to be achievable for heterogeneous cellular networks having hotspots and with delayed channel state information.
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An uplink-downlink two-cell cellular network is studied in which the first base station (BS) with $M_1$ antennas receives independent messages from its $N_1$ serving users, while the second BS with $M_2$ antennas transmits independent messages to its $N_2$ serving users. That is, the first and second cells operate as uplink and downlink, respectively. Each user is assumed to have a single antenna. Under this uplink-downlink setting, the sum degrees of freedom (DoF) is completely characterized as the minimum of $(N_1N_2+\min(M_1,N_1)(N_1-N_2)^++\min(M_2,N_2)(N_2-N_1)^+)/\max(N_1,N_2)$, $M_1+N_2,M_2+N_1$, $\max(M_1,M_2)$, and $\max(N_1,N_2)$, where $a^+$ denotes $\max(0,a)$. The result demonstrates that, for a broad class of network configurations, operating one of the two cells as uplink and the other cell as downlink can strictly improve the sum DoF compared to the conventional uplink or downlink operation, in which both cells operate as either uplink or downlink. The DoF gain from such uplink-downlink operation is further shown to be achievable for heterogeneous cellular networks having hotspots and with delayed channel state information.
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An uplink-downlink cellular network is studied in which the first base station (BS) with M 1 antennas receives independent messages from its N 1 serving users, while the second BS with M 2 antennas transmits independent messages to its N 2 serving users. Each user is assumed to have a single antenna. Under this uplink-downlink setting, the sum degrees of freedom (DoF) is completely characterized as the minimum of (N 1 N 2 + min(M 1 ,N 1 )(N 1 - N 2 ) + + min(M 2 ,N 2 )(N 2 -N 1 ) + )/ max(N 1 ,N 2 ), M 1 + N 2 ,N 1 + M 2 , max(M 1 ,M 2 ), and max(N 1 ,N 2 ), where a + denotes max(0, a). The result demonstrates that, depending on the network configuration, operating one of the cells as uplink and the other cell as downlink can improve DoF compared to the conventional uplink or downlink operation, in which both cells operate as either uplink or downlink.
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In most cellular systems, handover decisions are based on measurements of the downlink signal strength. When the average path gain in downlink and uplink is similar, such principles yield good performance in both directions of transmission. In cases with systematic imbalances between downlink and uplink however, it is not evident that the uplink performance is optimized. In this paper, a handover scheme based on a combination of downlink and uplink path gain measurements is outlined, and its performance is evaluated in a system with systematic downlink and uplink imbalances. As a reference, a downlink-based only mechanism is used. Results indicate that the combined scheme yields an insignificant gain in uplink signal to interference ratio (SINR). This gain is considerably lower than the corresponding loss in the SINR of users in the downlink. The reason for the low uplink gain is that uplink interference is higher in the cells with higher uplink/downlink imbalance ratio than in adjacent cells in equally loaded cells. As a result, users which are connected to cells with better uplink/downlink imbalance ratio than their adjacent cells also experience higher interference levels, which results in a limited gain in signal-to-interference ratio.
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Load balancing by proactively offloading users onto small and otherwise lightly-loaded cells is critical for tapping the potential of dense heterogeneous cellular networks (HCNs). Offloading has mostly been studied for the downlink, where it is generally assumed that a user offloaded to a small cell will communicate with it on the uplink as well. The impact of coupled downlink-uplink offloading is not well understood. Uplink power control and spatial interference correlation further complicate the mathematical analysis as compared to the downlink. We propose an accurate and tractable model to characterize the uplink SINR and rate distribution in a multi-tier HCN as a function of the association rules and power control parameters. Joint uplink-downlink rate coverage is also characterized. Using the developed analysis, it is shown that the optimal degree of channel inversion (for uplink power control) increases with load imbalance in the network. In sharp contrast to the downlink, minimum path loss association is shown to be optimal for uplink rate. Moreover, with minimum path loss association and full channel inversion, uplink SIR is shown to be invariant of infrastructure density. It is further shown that a decoupled association---employing differing association strategies for uplink and downlink---leads to significant improvement in joint uplink-downlink rate coverage over the standard coupled association in HCNs.
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Small cell technology significantly improves the coverage and boosts the capacity in Heterogeneous Cellular Network. And Cell Range Expansion technology makes average rate nearly optimal in downlink. However, because of large transmit power disparities of different kinds of base stations, uplink and downlink need to be considered as two different networks. In uplink, the problem is that many user equipments have to be associated with suboptimal base stations due to old Uplink-Downlink relationship. So we propose a new Uplink-Downlink relationship under which user equipments can be associated with optimal (may not the same) base stations in both directions. Numerical results demonstrate that performance under new Uplink-Downlink relationship has impressive gain in uplink coverage probability and average rate. Besides, when user equipments are all associated with their optimal base stations, network interference will be effectively mitigated through controlling uplink transmit power.
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Load balancing by proactively offloading users onto small and otherwise lightly-loaded cells is critical for tapping the potential of dense heterogeneous cellular networks (HCNs). Offloading has mostly been studied for the downlink, where it is generally assumed that a user offloaded to a small cell will communicate with it on the uplink as well. The impact of coupled downlink-uplink offloading is not well understood. Uplink power control and spatial interference correlation further complicate the mathematical analysis as compared to the downlink. We propose an accurate and tractable model to characterize the uplink SINR and rate distribution in a multi-tier HCN as a function of the association rules and power control parameters. Joint uplink-downlink rate coverage is also characterized. Using the developed analysis, it is shown that the optimal degree of channel inversion (for uplink power control) increases with load imbalance in the network. In sharp contrast to the downlink, minimum path loss association is shown to be optimal for uplink rate. Moreover, with minimum path loss association and full channel inversion, uplink SIR is shown to be invariant of infrastructure density. It is further shown that a decoupled association---employing differing association strategies for uplink and downlink---leads to significant improvement in joint uplink-downlink rate coverage over the standard coupled association in HCNs.
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