Feasibility Study of LTE Middle-Mile Networks in TV White Spaces for Rural India
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2016 IEEE 27th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications - (PIMRC): Mobile and Wireless Networks Feasibility Study of LTE Middle-Mile Networks in TV White Spaces for Rural India Chaitanya Prasad N†, Soubhik Deb†, Abhay Karandikar, Member, IEEE Department of Electrical Engineering Indian Institute of Technology, Bombay Email: [email protected], [email protected], [email protected] Abstract—With an intention to provide robust broadband To ensure coexistence of the TV broadcasters with the connection to rural areas, Government of India is laying out secondary devices, geolocation databases have been mandated optical fiber cables across the country connecting the rural by the regulators Federal Communications Commission and offices (named Gram Panchayat) under the initiative BharatNet. Office of Communications, UK [7]. Standards like IEEE This work explores the feasibility of implementing a middle-mile 802.11af, IEEE 802.22 have been designed for enabling network from these Gram Panchayats to the nearby villages, broadband wireless access in TV white spaces [7]. Extensive where wireless clusters will be set up, using LTE-Advanced over TV White Spaces owing to excellent propagation characteristics testbed trials have been pursued [8], [9], [10], [11] and of the frequencies in TV UHF band. A proportionally fair radio devices working on TV White Space have been developed resource allocation over the middle-mile network is proposed that [12]. Technologies are being conceptualized and developed for uses Coordinated Multipoint Technology offered by Long Term operation over TV white spaces in Long Term Evolution (LTE) Evolution - Advanced (LTE-A) which satisfies the broadband [13], [14], [15], [16]. It is estimated that around 40 MHz of requirement. The simulation results have shown that for a cell free UHF TVWS spectrum will be available for commercial radius of Coordination Region below 5 km, a rate of 1 Mbps use. Thus we analyze middle-mile network in this band. The per end-user for rural population density of India is achievable, major contributions of our work are: which is more than the 512 Kbps target rate prescribed by the Telecom Regulatory Authority of India (TRAI). Analyzed the feasibility of a middle-mile network employ- • Keywords—TV White Space, LTE-Advanced, middle-mile net- ing LTE-A technology over TV White Space for supple- works, resource allocation, proportionally fair menting broadband connection in India. This is the first time that estimates for the parameters like transmitter power, I. INTRODUCTION cell radius, etc., are determined based on targets set up by Telecom Regulatory Authority of India for broadband Digital age has brought immense opportunities for people. connections per subscriber. But due to the lack of broadband services, most of the Presented an iterative algorithm that assigns radio resources inhabitants of rural and semi-urban areas in India have been • for transmission between Gram Panchayat and its villages unable to exploit that opportunity. In a bid to assuage this based on individual average rates attained over previous problem, Government of India has been working on providing iterations so as to achieve proportional fairness. broadband access to 638, 619 villages via 250, 000 village offices called Gram Panchayat under the initiative BharatNet. The remainder of this paper is organized as follows. Gram Panchayats will be provided with Point of Presence Section II describes the system architecture. In Section III, (PoP) via optical fiber backhaul. Wireless clusters can be we discuss the problem statement and suggest radio resource formed at the villages for the last-mile access. Note that the allocation scheme for the same. The results of simulation villages are typically few kilometres away from the Gram described are in Section IV and based on that modifications for Panchayats. To solve the problem of backhauling the data from radio resource allocation scheme are suggested. Discussion on these clusters to the PoP, it is envisioned to use the under- the above results are provided in Section V. Finally, we draw utilized TV White Spaces (in the UHF band). out some concluding remarks in Section VI. The usage TV White Space for rural broadband is different in India from other countries primarily because: II. SYSTEM ARCHITECTURE Being located in Region 3 of International Telecommuni- As mentioned earlier, the connectivity between the PoP • cation Union (ITU) terrestrial spectrum allocations, Fixed, at Gram Panchayat and the wireless clusters in the villages Mobile, Broadcasting services is permitted in 470 590 can be provided using middle-mile network in the TV UHF MHz band which is in sharp contrast to services or− band band. An UHF Base Station (UHF-BS) will be connected to allowed in Europe and US [1]. the PoP and an UHF Customer Premise Equipment (UHF- [2] shows that in the 470 590 MHz band for four zones of CPE) will be connected to the access point of the wireless • India, at least 12 out of the− 15 channels (80%) are available cluster. From here on, UHF-BS and UHF-CPE will be referred in 100% of the areas which is much larger than that in US, to as just BS and CPE, respectively. The BS-CPE link uses UK, Europe [3], [4], [5], [6]. the LTE-A over TVWS spectrum and all theses links are combined to create a middle-mile network. For simplifica- † These authors contributed equally to this work. tion, only the downlink is considered. Antenna of each BS 978-1-5090-3254-9/16/$31.00 ©2016 IEEE 2016 IEEE 27th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications - (PIMRC): Mobile and Wireless Networks Fig. 2: Truncated network comprising of the central CoR and its associated Tiers I and II with 6 and 12 CoRs, repectively. Fig. 1: A simple overview of the two-stage system depicting where, PTx is the power of transmitting antenna on that PRB the connections among BSs, CPEs and end-users. Each CPU in dBm, GT x is the transmitting antenna gain in dBi, Noise handles RRA among a few selected SAs of adjacent BSs. comprises both thermal noise and interference from other BSs using the same PRB. The corresponding Spectral efficiency (SE) is evaluated from SINR using comprises of 3 sectoral antennas (SAs) identified by the set = 1, 2, 3 while the CPEs are directional antennas. Each SE = log10(1 + SINR), (2) S { } SA forms a sectoral angle of 120◦. Those SAs, belonging Using the Channel Quality Indicator (CQI) Table [18] and the to three adjacent BSs, which are facing each other form a diversity of the antenna being used, rate in a PRB of the Coordination Region (CoR). The CoRs also include the CPEs LOS link in a SubFrame of duration TSF =1ms for the that are associated to the SAs belonging to that CoR. The corresponding SE is obtained. The diversity φ is 1, 2, 4 for SAs forming a CoR coordinate to perform Radio Resource SISO, 2 2 MIMO and 4 4 MIMO, respectively. Allocation (RRA) of a set of Physical Resource Blocks (PRBs) ⇥ ⇥ = 1, 2, 3,...,K among the CPEs in with that CoR. III. RADIO RESOURCE ALLOCATION (RRA) LTE-AK { facilitates Coordinated} Multipoint (CoMP) Technology, which is employed for the resource allocation that ensures According to Telecom Regulatory Authority of India better performance using joint processing schemes. For its (TRAI), the current definition of broadband is 512 kbps implementation, a central processing unit (CPU) dedicated to connection which will be upgraded to a 2 Mbps≥ connection each CoR is established. This is illustrated in Fig.1. CoRs by 2017. If implementation of LTE-A over UHF TV White serve as a building block for our middle-mile network. We Space is supposed to be a good choice for middle-mile, then assume that the CoRs are arranged in cellular architecture it needs to ensure the above data rates at end-user. We first as shown for a truncated network in Fig. 2. The truncated formulate this objective and then suggest RRA for the same. network is with respect to the central CoR. The 6 adjacent CoRs closest to it form Tier I, next closest set CoRs forms A. Problem Formulation Tier II, and so on. Ideally, one has to analyze an infinite network but for the scope of distances involved in middle- Following notations are used in rest of the work: mile network, analyzing the truncated network is found to max Pb : Maximum transmission power of BS b be sufficient. Fixing a central CoR, the set of CoRs in the • k Pbs : Power of BS b in sector s on PRB k truncated network is = CoR1,...,CoR19 and set of • k M { } r(m,n) : Received rate of CPE(m,n) on PRB k CPEs in some CoRm is represented by m. A CPE in • is depicted by CPE2M . But it is possibleN that during Nm (m,n) The objective is to maximize rm under total power constraint. allocation of PRBs not all CPEs are eligible. The set of legally Mathematically, available CPEs for resource allocation in CoRm is denoted k by ⇤ . Assume that there is always data to be transmitted. max r m : CoR , (3) Nm (m,n) 8 m 2M The Channel State Information (CSI) for each BS-CPE link is n:CPE(m,n) m k assumed to be available at the CPU. X 2N X2K subject to: P k P max, bs b A large part of India is flat terrain. Hence, BS sectoral s k X2S X2K antenna at height of 12 15 m and CPE antenna at height P k 0. of 5 m is considered for− this work. Hata Model [17] is most bs ≥ appropriate for this terrain in 470 590 MHz band.