Novel radio cellular design improving capacity and mobility performance for advanced cellular networks

Computers and Electrical Engineering xxx (2015) xxx–xxx

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Novel radio cellular design improving capacity and mobility performance for advanced cellular networks q Leila Aissaoui Ferhi ⇑, Kaouthar Sethom, Fethi Choubani, Ridha Bouallegue InnoV’Com Laboratory, Higher School of Communications (SUP’COM), Technology City of Communications, Raoued Road Km 3.5, 2083 El Ghazala, Ariana, Tunisia

a r t i c l e

i n f o

Article history: Received 2 October 2014 Received in revised form 21 July 2015 Accepted 23 July 2015 Available online xxxx Keywords: LTE-A Horizontal sectorization Vertical sectorization Carrier aggregation Throughput Mobility

a b s t r a c t This paper studies sectorization increase in horizontal and vertical plane. We have simulated downlink (DL) macro long-term evolution (LTE) network using three-dimensional antenna and propagation models. New network layouts have been proposed based on 4-sector site deployment. The challenge was to offer lower network cost and complexity. Simulation results have showed good tradeoff between capacity and mobility performance in comparison to known sectorization schemes. Besides, carrier aggregation (CA) and active antenna system (AAS) have been used to exploit the sector vertical plane. Low frequency band (800 MHz) improves coverage and indoor signal penetration in urban environment. Our proposed sectorization schemes give multi-objective network quality of service (QOS). Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction The number of mobile broadband subscribers worldwide increases perpetually and grew about 7% year-on-year during quarter1 2014. The number of subscriptions increased faster with 35% year-on-year, attaining 2.3 billion. Devices were mostly smartphones leading to mobile data traffic growth of 65% between quarter1 2013 and quarter1 2014 [1]. According to CISCO, mobile data traffic will grow at compound annual growth rate of 61% from 2013 to 2018, reaching 15.9 exabytes per month by 2018 [2]. Aiming to satisfy the forecast traffic demand and enhance the user experience, a new generation of mobile cellular network third generation partnership project (3GPP)’s LTE has been deployed. Research projects are in progress in order to reach fourth generation (4G) requirements and to fulfill the huge traffic demand especially in dense urban and indoor environments. Actually, work is deeply addressed to optimize LTE-Advanced (LTE-A) as defined from release 10 onwards. In LTE-A, focus is on higher capacity. The driving force to further develop LTE toward LTE-A was to provide higher bitrates in a cost efficient way. The main new functionalities introduced in LTE-A are support of relay nodes, enhanced use of advanced antenna techniques and CA [3]. Traditionally, network capacity expansion is done by deploying new conventional 3-sector sites and small cells. As a result, operator must assume more system complexity, high backhaul resources and difficult networking of numerous low-power base stations (BS). AAS is an advanced antenna technique providing electronic beam control in the vertical plane. Every beam has its own antenna tilt. Indeed, it is possible to split cell into inner and outer cells, called vertical sectorization (VS). The total available radio resources are doubled and

q

Reviews processed and recommended for publication to the Editor-in-Chief by Associate Editor Dr. M.H. Rehmani.

⇑ Corresponding author. Tel.: +216 71 857 000; fax: +216 71 856 829. E-mail address: [email protected] (L. Aissaoui Ferhi). http://dx.doi.org/10.1016/j.compeleceng.2015.07.019 0045-7906/Ó 2015 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Aissaoui Ferhi L et al. Novel radio cellular design improving capacity and mobility performance for advanced cellular networks. Comput Electr Eng (2015), http://dx.doi.org/10.1016/j.compeleceng.2015.07.019

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the total transmit power is split between inner and outer cells. The use of AAS enhances system coverage and capacity at lower network deployment cost. Previous research results on high order sectorization (HOS) use conventional 3-sector, 6-sector and 12-sector network layouts for additional horizontal sectorization (HS). The vertical plane of conventional 3-sector network layout is used for VS. In this paper, new sectorization schemes based on 4-sector site are proposed and simulated for DL frequency division duplexing (FDD) macro LTE-A network using three-dimensional antenna and propagation models. Some CA scenarios use low frequency band 800 MHz. To our knowledge, such 4-sector cellular design using VS and CA is not currently available in literature. Our challenge was to find good tradeoff between network capacity and mobility performance. The paper is organized as follows: Section 2 gives an overview of previous research works on increased HS and VS for cellular networks. System model and simulation assumptions are deeply discussed in Section 3. Simulation results of studied network layouts are given in Section 4. Finally, the work is concluded in Section 5.

2. Related work High order HS is well known in cellular mobile networks as an important design technique to increase capacity. As mentioned in [4], wideband code division multiple access (WCDMA) network deployment is based on 3-sector sites in baseline configuration. Six-sector sectorization increases the capacity. Rather than adding new sites to the network, the addition of sector to existing sites requires lower investment and less deployment time. A cost comparison between sectorization and new site deployment is given in Table 1. Studies presented for WCDMA network in [5] concluded that HOS gives more capacity. Nevertheless, the enhancement is not proportional to the number of sectors due to antenna radiation pattern overlapping. In fact, increasing the sectorization from single sector to three sectors leads to capacity increase of 2.8. Similarly, increasing the sectorization from three sectors to six sectors ensures a capacity gain of approximately 1.8. Simulations in [6] investigated two network site topologies: six-sectors and twelve-sectors. Results showed a sectorization capacity enhancement for large inter-site distance (ISD). In densely populated cells with low angle spread, 12-sector site achieves similar capacity performance like conventional 3-sector site with multiuser multiple input multiple output transmission. Studies in [7] compared overlapping between sectors for LTE network. It is about 144° for 3-sector configuration and 192° for 6-sector configuration. High overlapping leads to dangerous inter-cell interference level. Inter-cell interference coordination (ICIC) feature is recommended for efficient use of 6-sector layout. Moreover, installation complexity is also a main disadvantage to deploy 6-sector network configuration in urban area. Previous HOS studies show essentially its capacity gain. However, HS increase induces expensive costs (antennas, feeders, duplexers, base stations, transmission equipments, etc.) and complex installation procedures. In reality, each operator minimizes expenses and seeks technical solutions at reasonable cost, lower complexity and significant gain. For HOS, increasing sector number is not always proportional to capacity gain and it can be worse if ICIC feature is not implemented as mentioned in [7]. Besides, the typical beamwidth and sidelobe attenuation for 3-sector antenna pattern are 65° and 20 decibel (dB) as for the 6-sector antenna pattern 33° and 23 dB. So, half power beam width (HPBW) must be very narrow with 6-sector network configuration. It is commonly known that narrow beams lead to higher antenna gain but to bigger antenna dimensions. Big antenna dimensions are not applicable in urban environment. Later trends (3GPP release 10 and beyond) encourage even multi-operator and multi-layer cell layouts increasing already antenna ports [8]. Furthermore, mobility efficiency is one of the most important network performance indicators. HS impacts mobility performance and increases dramatically handover flow. In HOS context, mobility behavior is not yet simulated to follow up optimized radio sector design for an LTE network. Works in [9] presented capacity gain results from simulation and real world deployment of HOS (3, 6, 9, 12 and 15 sectors) when applied to an evolved high speed packet access network. Nevertheless, handover signaling over the Iub interface had more than doubled or quadrupled when going from 3 to 6 or from 3 to 12 sectors, respectively. Similarly, handover flow of an LTE-A network can significantly increase. Recently, there has been a growing interest to try increased sectorization in vertical plane using AAS. As described in [10], VS seems to be an attractive capacity providing more flexibility (carrier-specific tilting, system-specific tilting, etc.) and less installation constraints. In VS case (Fig. 1), two separate beams (inner and outer cells) are arranged with distinct antenna parameters. VS has been simulated in [11] for WCDMA network using two propagation models. It has been showed that serving area size of inner sector is a critical parameter to ensure VS performance gain. It has been recommended to use three-dimensional propagation modeling to get more realistic and better performance. Work in [10] has studied simultaneous horizontal and vertical HOS for conventional 3-sector cellular layout 3GPP case1 and case3 for LTE network. VS scheme has been referred to as VS 3  2 network. For various combinations of antenna parameter, VS 3  2 showed promising UE and cell throughput gain. In [12], VS depends on parameters like inter-site distance (ISD), tilt range and spatial UE distribution. It has been proven Table 1 Cost comparison.

New site deployment Sectorization

New eNodeB

New power resources

New transmission equipments

Antenna number

Time of deployment

Renting cost

Yes

Yes

Yes

3 per site

Long

Yes

No

No

No

1 per sector

Few

No

Please cite this article in press as: Aissaoui Ferhi L et al. Novel radio cellular design improving capacity and mobility performance for advanced cellular networks. Comput Electr Eng (2015), http://dx.doi.org/10.1016/j.compeleceng.2015.07.019

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Fig. 1. Vertical sectorization [10].

that HS gives higher capacity gain than VS for conventional sector layout. Investigations in [13] show important capacity gain for VS and 2 GHz-CA capable network. As defined by 3GPP (Fig. 2), CA is used in LTE-A in order to increase the bandwidth, and thereby increase the bitrate. Each aggregated carrier is referred to as a component carrier (CC). The CC can have a bandwidth of 1.4, 3, 5, 10, 15 or 20 MHz. Five CCs at most can be aggregated. Hence, the maximum aggregated bandwidth is 100 MHz. With CA, it is possible to schedule a UE on multiple CCs simultaneously. Thus, it is possible to reach higher cell and UE throughput. There are three CA combinations: intra-band contiguous, intra-band non-contiguous and inter-band (see Fig. 2). 3. System model and simulation assumptions 3.1. Reference network model We have considered DL FDD macro LTE-A homogenous network deployment in urban environment. Parameters are taken according to 3GPP recommendations for performance evaluation of LTE advanced technologies [8,14]. 3GPP hexagonal cellular layouts case1 and case3 have been chosen. Network layouts are formed by 19 eNodeBs. The network is assumed to be single-carrier, operating at 2 GHz and having a bandwidth of 10 MHz. Each eNodeB is typically 3-sector site and therefore the network is referred to as 3  1 reference network layout. Two ISDs have been adopted in accordance to 3GPP case1 network topology (ISD = 500 m) and to 3GPP case3 network topology (ISD = 1732 m) [8,14]. User equipments (UE) are uniformly distributed. Physical resource blocks (PRB) per sector are equally shared between users (full buffer traffic). Sixty users are assigned per site and are uniformly scaled per sector number, resulting in 20 UEs/sector for 3-sector site. Antennas and propagation loss are three-dimensional modeled. Horizontal antenna pattern (AH) and vertical antenna pattern (AV) are derived from 3GPP case1 and case3 (macro cell) system simulation baseline parameters:

"  #  u 2 AH ðuÞ ¼  min 12 ; Am

ð1Þ

u3 dB

"

#  2 h  hetilt AV ðhÞ ¼  min 12 ; SLAv h3 dB

ð2Þ

with Am = 25 dB, SLAv = 20 dB.

Fig. 2. Carrier aggregation [3].

Please cite this article in press as: Aissaoui Ferhi L et al. Novel radio cellular design improving capacity and mobility performance for advanced cellular networks. Comput Electr Eng (2015), http://dx.doi.org/10.1016/j.compeleceng.2015.07.019

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L. Aissaoui Ferhi et al. / Computers and Electrical Engineering xxx (2015) xxx–xxx Table 2 RWP model parameters. Parameters

Value

Simulation time (s) Speed interval (m/s) Pause interval (s) Walk interval (s) Direction interval (degrees) Total network UE number

500 [0.2 2.2] [0 1] [2 6] [180 180] 1140

Where Am is the front-to-back attenuation and SLAv is side lobe attenuation. The parameter hetilt is the electrical antenna tilt. The values hetilt = 15° has been used for 3GPP case1 and hetilt = 6° has been used for 3GPP case3. Estimation of three-dimensional antenna pattern from two perpendicular cross-sections azimuth and elevation patterns is defined as shown below:

Aðu; hÞ ¼  minf½AH ðuÞ þ AV ðhÞ; Am g

ð3Þ

The path-loss is calculated using the equation:

LðRÞ ¼ 128:1 þ 37:6 Log10ðRÞ

ð4Þ

L is the path-loss in dB, R is the distance (in kilometers) between site and UE. Mobility model is needed to estimate UE move. The random waypoint (RWP) model is a commonly used mobility model for wireless network simulations [15]. RWP model has been used in our work to simulate handover flows. RWP assumptions are as shown in Table 2. As mentioned in [16], handover (HO) is triggered at the UE based on parameters defined by the network. We notice ‘‘hysteresis’’ and ‘‘Time To Trigger’’ (TTT) parameters. The UE makes periodic measurements of reference signal received power (RSRP) and reference signal received quality (RSRQ) received from the serving cell and from the strongest adjacent cells. Handover decision can be based on RSCP (A3 event) or RSRQ (A5 event). In our work, we have chosen RSCP criteria. If handover decision is based on RSRP, handover is triggered when neighbor cell RSRP value is higher than serving cell RSRP by a value of ‘‘HO hysteresis’’ dBs. This condition has to be satisfied for a period of time equal to TTT millisecond (ms). An example of HO triggering within 3GPP LTE is illustrated in Fig. 3. 3.2. Proposed network model and simulation parameters A good network design has to maintain a tradeoff between cost, installation flexibility and global performance to be profitable for operators. From this point of view, we have proposed customized HS and VS increase for an LTE-A network. Our

Fig. 3. RSCP based handover.

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L. Aissaoui Ferhi et al. / Computers and Electrical Engineering xxx (2015) xxx–xxx

Three sector network layout

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Please cite this article in press as: Aissaoui Ferhi L et al. Novel radio cellular design improving capacity and mobility performance for advanced cellular networks. Comput Electr Eng (2015), http://dx.doi.org/10.1016/j.compeleceng.2015.07.019

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objective was to find multi-objective optimized radio design providing cost, coverage, capacity and mobility gains. We have chosen: – To evaluate increased HS by comparing three network layouts: reference three-horizontal sector (3  1), new proposed four-horizontal sector (4  1) and six-horizontal sector (6  1) site deployments (Figs. 4–6). 3  1and 6  1 sector deployments were treated in previous works. – To measure the gain of VS applied to already HS layouts (reference 3  1, new 4  1 and 6  1). – To highlight mobility behavior within increased HS/VS. Mobility behavior is rarely treated in high-order sectorization context in literature. High-order sectorization has been usually evaluated regarding to throughput gain it can offer. – To apply LTE-A feature CA in intra-band and inter-band fashion.

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– To highlight benefit of low frequency band 800 MHz, actually occupied by television service in many countries, forecast to be candidate for future LTE network. Frequency band 800 MHz is considered as gold frequency band ensuring better indoor signal penetration. In the open literature, this band is not yet used in a VS investigation context. In this paper, 800 MHz frequency band has been used in our proposed VS schemes. Reference network model 3  1 is used as reference network layout to evaluate and compare our proposed sectorization schemes. It is a basic network configuration that can be expanded in terms of radio resources (sector, carrier, etc.) and features (CA, VS, etc.). Our proposed network model uses the same network cluster similarly to reference network model and includes additional HS and VS schemes. Cluster sites are homogeneous and equally sectorized. The considered network scenarios are CA capable. Scenarios can be single carrier (SC) or dual carrier network with use of two frequency bands: 2 GHz and 800 MHz. Indeed, system bandwidth is 10 MHz for SC network scenarios and 20 MHz for CA based network scenarios (intra-band and inter-band). One CC is assigned to each vertical sector. UE benefits simultaneously from radio resources of both inner and outer vertical sectors. In our work, two CA scenarios have been investigated: contiguous intra-band 2–2 GHz CA (IBC-CA) and inter-band non contiguous 2 GHz–800MHz CA (IBD-CA). We suggest nine network layouts. 31 41 61 32 32 32 42 42 42

HS: based on three-horizontal sectors per site HS: based on four-horizontal sectors per site HS: based on six-horizontal sectors per site SC VS: based on three-horizontal sectors per site. SC VS is applied IBC-CA VS: based on three-horizontal sectors per site. VS and IBC-CA are applied IBD-CA VS: based on three-horizontal sectors per site. VS and IBD-CA are applied SC VS: based on three-horizontal sectors per site. IBC-CA VS: based on three-horizontal sectors per site. VS and IBC-CA are applied IBD-CA VS: based on three-horizontal sectors per site. VS and IBD-CA are applied

We notice that 3  1 HS, 6  1 HS, 3  2 SC VS and 3  2 IBC-CA VS network layouts have been treated in previous works. Layouts 4  1 HS, 4  2 SC VS, 4  2 IBC-CA VS and 4  2 IBD-CA VS are our new proposed sectorization schemes. Three-sector and four-sector cellular layouts have been considered for both 3GPP case1 and case3. VS have been treated according to 3 scenarios: using same frequency, using 2 intra-band contiguous 2 GHz CCs and using 2 inter-band 800 MHz/2 GHz non-contiguous CCs. Simulation parameters are used according to each frequency band and carrier aggregation requirements. VS is ensured by antenna tilt change of each vertical sector pair. We have used same VS modeling as described in [10]. For VS proposed schemes, transmission power of each cell is equally shared between inner and outer cells.

Table 3 Simulation assumptions. Parameter

Simulation values

3GPP reference network layouts Environment Cellular layout Sectorization schemes

3GPP case1, 3GPP case3 Macro cell, Urban area Hexagonal grid, 19 eNodeBs 3  1 HS, 4  1 HS, 6  1 HS, 3  2 SC VS, 3  2 IBC-CA VS, 3  2 IBD-CA VS, 4  2 SC VS, 4  2 IBC-CA VS, 4  2 IBD-CA VS (800; 2000) MHz (10; 20) MHz 1 60 UEs per site 50; 100 (500, 1732) m 32 m 1.5 m L(R) = 119.8 + 37.6 Log10(R); L(R) = 128.1 + 37.6 Log10(R), R in kilometers

System frequency System bandwidth (1 CC; 2CCs) Frequency reuse factor Number of UEs Number of PRBs (1 CC; 2CCs) Inter-site distance Site height UE height Propagation loss model (800 MHz; 2 GHz) Shadowing standard Penetration loss Transmitted power (1 CC; 2CCs) Antenna technique Horizontal HPBW Vertical HPBW Antenna gain Feeder loss (800 MHz; 2 GHz) Thermal noise Traffic distribution Traffic model Scheduling

8 dB 20 dB (43; 46) dB m per vertical sector Single input single output (SISO) 65°, 45°, 33° for respectively 3-sector, 4-sector and 6-sector layouts 6.8° Calculated based on antenna characteristics 0.25; 2 dB 174.0 dB m Uniform Full buffer Round-Robin

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Ptotal ¼ Pinner þ Pouter

ð5Þ

where Ptotal is total transmission power per cell. Pinner and Pouter are the transmission power of respectively inner and outer vertical sector. For SC and CA based network scenarios, the amount of resources are doubled but the power per PRB is halved (Ptotal = 46 dB m; Pinner = Pouter = 43 dB m). System bandwidth is 10 MHz. Two frequency bands: 2 GHz and 800 MHz have been used to highlight low frequency coverage gain. For intra-band CA based network scenarios, we have used 2 GHz IBC-CA in a VS fashion. As recommended by 3GPP in [17], a total transmission power of 49 dBm can be used. The amount of resources are doubled and the power per physical resource block (PRB) is halved (Ptotal = 46 dBm). System bandwidth is 20 MHz and UE is simultaneously connected to the two CCs.

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For inter-band CA based network scenarios, we have used 2 GHz–800 MHz IBD-CA in a VS fashion. A total transmission power of 49 dB m has been used. Inner sector and outer sector take 2 GHz CC and 800 MHz CC, respectively. The amount of resources are doubled and the power per PRB is halved (Ptotal = 46 dBm). System bandwidth is 20 MHz with coverage advantage of 800 MHz. UEs are simultaneously connected to two CCs while there is a good coverage for both CCs. Otherwise, the user is connected to outer CC thanks to its larger radius. Similarly to 3  1 reference model, sixty users are assigned per site and uniformly scaled per sector according to the number of sectors per sectorization scheme. So, capacity gain of HS and VS per site and per user can be perceived.

Please cite this article in press as: Aissaoui Ferhi L et al. Novel radio cellular design improving capacity and mobility performance for advanced cellular networks. Comput Electr Eng (2015), http://dx.doi.org/10.1016/j.compeleceng.2015.07.019

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Estimation of three-dimensional antenna pattern, mobility model, handover triggering and 2 GHz path-loss model are identical to the reference network model. For 800 MHz frequency band, the path-loss is calculated using the equation:

LðRÞ ¼ 119:8 þ 37:6 Log10ðRÞ

ð6Þ

L is the path-loss in dB, R is the distance (in kilometers) between site and UE. In our work, HO hysteresis = 6 dB and TTT = 320 ms [18]. Calculated metrics are total network handover number, intra-eNodeB handover number and inter-eNodeB handover. At each hard handover, a drop occurs during ‘‘handover interruption time’’ = 10.5 ms [17]. Thus, high number of handovers degrades network quality of service. All simulation parameters are summarized in Table 3.

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X-axis (m) Fig. 9. 3GPP case3 6-sector cellular layout.

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System performance has been calculated in terms of DL received signal strength, best server distribution, DL SINR, DL throughput and total handover number. Matlab has been used to develop an LTE-A network simulator. Parameters are taken according to 3GPP recommendations for performance evaluation of LTE advanced Technologies [8,14]. 4. Results discussions 4.1. Increased HS In this section, the performance gain of additional HS to 2 GHz SC network (3  1 reference network layouts) is evaluated. In both 3GPP case1 and 3GPP case3, more interference is perceived. It is due to additional horizontal sectors making SINR worse for 4  1 HS and 6  1 HS layout compared to 3  1 layout. The received signal strength distribution is better for Received signal strength (dBm) 3000

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Please cite this article in press as: Aissaoui Ferhi L et al. Novel radio cellular design improving capacity and mobility performance for advanced cellular networks. Comput Electr Eng (2015), http://dx.doi.org/10.1016/j.compeleceng.2015.07.019

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HOS because antenna number per site increases. If sector number per site increases, sector service area is narrower. In fact, narrower antenna HPBW (45° for 4  1 HS cellular layout, 33° for 6  1 HS cellular layout) are needed and there are more serving cells in the network (Figs. 5–10). Despite the SINR decreases at higher HS, the additional radio resources improve site throughput. The average site throughput is defined as the sum of average throughput of all sectors within the site. As highlighted in Figs. 11 and 12, we note an average throughput enhancement of 25.67% and 74.68% for 4  1 HS layout for respectively 3GPP case3 and 3GPP case1. For 6  1 HS layout, throughput gain is about 76.61% and 160.22% for respectively 3GPP case3 and 3GPP case1 6  1 HS layout. 3GPP case1 throughput outperforms 3GPP case3 one because cell edge throughput is worse for large ISD (1732 m for 3GPP case3 and 500 m for 3GPP case1). From a throughput gain point of view, 6  1 HS layout seems to be the best radio design configuration. Nevertheless, our work looks also to mobility performance in HOS context, not deeply treated in the open literature for LTE-A network. Figs. 11 and 12 show an increase of the total network handover number of 31.56% and 19.34% for 4  1 HS layout for respectively 3GPP case3 and 3GPP case1. For 6  1 HS cellular layout, total network handover number increases by 134.32% and 70.24% for respectively 3GPP case3 and 3GPP case1 6  1 HS site deployment. We conclude that 6  1 HS site deployment is the best-throughput densification solution in comparison to 3  1 HS and 4  1 HS site deployment. However, it generates a lot of handover overhead. Higher number of horizontal sectors expands overlapping areas and pushes UEs to handoff more frequently. In fact, 4  1 HS layout has reasonable increase of handover flow. However, 6  1 HS has dangerous handover number. As mentioned in [19], only hard handover is supported in LTE. The handover performance in terms of success rate and delay of execution is very important since each handover creates an interruption time in the user plane (=10.5 ms). So, high number of handovers generates more drop periods or ‘‘interruption time’’ mandatory at each handover triggering. During an ‘‘interruption time’’, seamless services cannot be supported and users have to suffer from bad QOS. In 3GPP case3 having high ISD (=1732 m), the number of handover is high due to pilot pollution in cell edge. We have also treated intra-eNodeB and inter-eNodeB handover behavior in our work. Intra-eNodeB handover is a handover within one sector or between different sectors of the same eNodeB. Inter-eNodeB handover is a handover between different eNodeBs. Indeed, inter-eNodeB handover causes additional system overhead and more latency to users compared to intra-eNodeB handover. For 3GPP case3, 4  1 HS layout presents the same trend as conventional 3  1 HS layout. It has 37% of intra-eNodeB handovers and 62% of inter-eNodeB handover. However, we notice an increase of 63.47% of intra-eNodeB handovers for 6  1 HS layout. It is expected as the number of sectors per site is high and the ISD is large (see Fig. 13). For 3GPP case1 having lower ISD, 6  1 HS layout and 6  1 HS layout have the same intra-eNodeB and inter-eNodeB handover percentage split. We notice good performance for 4  1 HS layout. In fact, intra-eNodeB handover percentage increases to 47.30% versus 34.59% for 3  1 HS layout. In addition, the increase of total handover number remains reasonable as mentioned in Fig. 14. In comparison to conventional 3  1 and 6  1 HS layouts, our new 4  1 HS cellular layout is the best radio design in terms of intra-eNodeB and inter-eNodeB handover balance especially for 3GPP case1 modeling urban environment. Taking mobility efficiency into account, 4  1 HS layout shows better cost and global performance efficiency tradeoff than 3  1 HS and 6  1 HS cellular layouts. In addition, 4  1 site installation is less complicated than 6  1 site. As a result, we recommend 4  1 HS cellular layout as a radio densification solution for urban/suburban area offering higher capacity, safe mobility behavior and less installation constraints. It should be noted that conventional 3  1 layout is not always the best choice. It depends on coverage and capacity goals of the planned area. For example, 2-horizontal sector cellular layout is an efficient sectorization scheme to cover roads and highways. 4.2. Increased vertical sectorization We have investigated VS for already treated HS schemes (3  1 HS, 4  1 HS) using 3GPP case1 cluster and 3GPP case3 cluster. VS was not tested for 6  1 HS layout because it is a dangerous radio design in terms of mobility performance. VS scenarios includes SC and CA based network cases.

Fig. 11. 3GPP case3 throughput and mobility performance for 3 cellular layouts.

Please cite this article in press as: Aissaoui Ferhi L et al. Novel radio cellular design improving capacity and mobility performance for advanced cellular networks. Comput Electr Eng (2015), http://dx.doi.org/10.1016/j.compeleceng.2015.07.019

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Fig. 12. 3GPP case1 throughput and mobility performance for 3 cellular layouts.

Fig. 13. 3GPP case3 intra/inter eNodeB handover percentage split.

Fig. 14. 3GPP case1 intra/inter eNodeB handover percentage split.

For single carrier (2 GHz) 3GPP case1 cluster, 3  2 SC VS causes bad network performance as showed in Fig. 15. Aggressive interference is measured leading to worse SINR compared to conventional 3GPP case1 (3  1). Network is mostly covered by inner cells. Inner cell coverage percentage is 100% per horizontal sector for all cluster central sites and outer cells cover only border area. Outer cells are mostly network interferers and do not achieve significant capacity gain. Average inner cell, outer cell and site throughput are respectively equal to 6.49 Mbps, 1.76 Mbps and 20.86 Mbps. Compared to average site throughput followed up for conventional 3GPP case1 (30.33 Mbps), we notice a throughput loss of 31.23%. In a SC deployment context, we conclude that VS degrades network performance and does not bring capacity gain for short ISD network configuration. Please cite this article in press as: Aissaoui Ferhi L et al. Novel radio cellular design improving capacity and mobility performance for advanced cellular networks. Comput Electr Eng (2015), http://dx.doi.org/10.1016/j.compeleceng.2015.07.019

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For single carrier (2 GHz) 3GPP case3 cluster, 3  2 SC VS and 4  2 SC VS network layouts have been studied. First, 3  2 SC VS seems to be more effective for 3GPP case3 due to large ISD providing two acceptable inner and outer cell service areas (see Fig. 16). Inner cell coverage area is well recognized. The average inner cell coverage percentage is equal to 35.61% per horizontal sector. We note a site throughput average of 54.04 Mbps corresponding to 27.27% throughput gain in comparison to conventional 3GPP case3 network layout. For mobility concern, the total network handover number is equal to 530 marking a little increase of 4.53%. Thus, a normal handover flow is maintained. We conclude that 3  2 SC VS is better than 6  1 HS to achieve mutual capacity and mobility performance.

Please cite this article in press as: Aissaoui Ferhi L et al. Novel radio cellular design improving capacity and mobility performance for advanced cellular networks. Comput Electr Eng (2015), http://dx.doi.org/10.1016/j.compeleceng.2015.07.019

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Second, we propose new SC VS scheme 4  2 SC VS based on our new 4  1 HS scheme. Indeed, additional HS and VS have been jointly used (Fig. 17). In 4  2 SC VS layout, we have 4 inner cells and 4 outer cells per site. Inner cell coverage percentage is equal to 35.17% per horizontal sector similarly to 3  2 SC VS layout. Capacity gain is interesting. In fact, an average site throughput of 62.24 Mbps has been measured. It is an increase of 49.34%, 18.83% and 15.16% in comparison to respectively conventional 3GPP case3, 4  1 HS layout and 3  2 SC VS layout. As VS splits horizontal sector to inner cell and outer cell, average network handover number has slightly increased. Indeed, we note a handover number equal to 690 corresponding to handover increase of 36.09%, 3.45% and 30.19% compared to conventional 3GPP case3, 4  1 HS and 3  2 SC VS network configurations, respectively. However, 4  2 SC VS network layout mobility behavior is more efficient than 6  1 HS and proving a gain of 41.92% seen against 6  1 HS layout. In SC network deployment, our new proposed 4  2 SC VS network configuration offers best capacity and mobility performance by optimally joining HS and VS. For VS based on IBC-CA, we suppose that users are simultaneously connected to both inner and outer cell. In fact, they have approximately the same geographic service area due to the use of same tilt and contiguous carriers. Received signal strength CDF of 3  2 IBC-CA VS and 4  2 IBC-CA VS network configurations are very near as shown in Fig. 18. First, 3  2 IBC-CA VS network layout simulation results showed an average site throughput equal to 96.29 Mbps. It is an improvement of 131.05%, 83.85%, 30.83%, 78.18% and 54.71% compared to respectively conventional 3GPP case3, 4  1 HS, 6  1 HS, 3  2 SC VS and 4  2 SC VS network configurations. Mobility performance is marked by good average network handover number equal to 570. Second, 4  2 IBC-CA VS network layout simulation results showed an average site throughput equal to 125.4 Mbps. It is an improvement of 200.89%, 139.42%, 70.38%, 132.05%, 101.48% and 30.23% compared to respectively conventional 3GPP case3, 4  1 HS, 6  1 HS, 3  2 SC VS, 4  2 SC VS and 3  2 IBC-CA VS network layouts. Mobility performance is marked by good average network handover number equal to 595.

Please cite this article in press as: Aissaoui Ferhi L et al. Novel radio cellular design improving capacity and mobility performance for advanced cellular networks. Comput Electr Eng (2015), http://dx.doi.org/10.1016/j.compeleceng.2015.07.019

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We advise IBC-CA VS (2 GHz CC, 2 GHz CC) to cover urban area needing maximum capacity to solve frequent congestion and to enhance customer experience. For VS based on IBD-CA, inner cell is configured with 2 GHz CC and outer cell with 800 MHz CC. We suppose that users are simultaneously connected to both inner and outer cell when both cells have good coverage. Otherwise, UE is connected to only 800 MHz CC having larger coverage. It is noted that same antenna tilt is assigned to both vertical sectors. Network layouts 3  2 IBD-CA VS and 4  2 IBD-CA VS have been investigated. First, 3  2 IBD-CA VS layout simulation results showed an average site throughput equal to 111.42 Mbps. It is an increase of 167.35%, 112.73%, 51.38%, 106.18%, 79.02% and 15.71% compared to respectively conventional 3GPP case3, 4  1 HS, 6  1 HS, 3  2 SC VS, 4  2 SC VS and 3  2 IBC-CA VS network configurations. For tested inter-band non contiguous CCs, received signal strength distribution is better than intra-band contiguous CCs (see Fig. 18). This coverage enhancement is derived from better signal penetration of 800 MHz frequency band. Low frequency band provides larger cell radius and makes border areas (rural or sub-urban areas) well covered. The average network handover number increases slightly to 598 due to larger outer cells. Second, our new proposed sectorization scheme 4  2 IBD-CA VS network layout simulation results showed an average site throughput equal to 121.6 Mbps. It is an increase of 191.78%, 132.17%, 65.21%, 125.02%, 95.37%, 26.29% and 9.14% compared to respectively conventional 3GPP case3, 4  1 HS, 6  1 HS, 3  2 SC VS, 4  2 SC VS, 3  2 IBC-CA VS and 3  2 IBD-CA VS network configurations. Similarly to 3  2 IBC-CA VS network layout, Fig. 18 shows better received signal strength distribution of 800 MHz CC. The average network handover number increases to 770 as a result of signal overshooting of 800 MHz CC. We advise IBD-CA (800 MHz CC, 2 GHz CC) for sub-urban area needing capacity and wide coverage. It is also very efficient for urban areas thanks to better indoor signal penetration of 800 MHZ CC. However, careful down-tilting and power tuning must be applied to avoid signal overshooting and to ensure good best server distribution. Fig. 19 summarizes the proposed network layouts for 3GPP case3. It is obvious that network layouts, having both HS and VS, offer the best radio network performance in term of coverage, throughput and handover flow. Our new proposed

Please cite this article in press as: Aissaoui Ferhi L et al. Novel radio cellular design improving capacity and mobility performance for advanced cellular networks. Comput Electr Eng (2015), http://dx.doi.org/10.1016/j.compeleceng.2015.07.019

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Fig. 19. Proposed network layouts comparison.

sectorization schemes: 4  2 IBC-CA VS and 4  2 IBD-CA VS are strongly recommended to boost capacity and maintain mobility performance for urban and sub-urban LTE-A and beyond advanced cellular networks. 5. Conclusion and future work Due to data traffic growth and limited radio resources, operators must optimize the macro sites and spectrum usage to satisfy customer needs. Lack of spectrum, expensive macro BS and poor indoor coverage degrades enormously the perceived QOS. HOS seems to be a cost effective radio densification alternative. HOS solutions exploit the full potential of deployed and forecast network sites. Thus, it is possible to delay the implementation of costly and complex densification solutions like additional deployed sites and small cells. HOS can be HS or VS. We have investigated HOS impact in both horizontal and vertical plane for LTE-A macro network. Results have been obtained based on simulations of many HS and VS schemes for SC and CA capable network scenarios operating at 2 GHz and 800 MHz frequency bands. New network layouts based on four-horizontal sector have been proposed (4  1 HS, 4  2 SC VS, 4  2 IBC-CA VS and 4  2 IBD-CA VS) and compared to known HS and VS layouts (3  1 HS, 6  1 HS, 3  2 SC VS, 3  2 IBC-CA VS and 3  2 IBD-CA VS). A multi-objective radio performance goal: coverage, capacity and mobility has been attained. According to the reached results, increased HS and VS boost the data throughput but handover performance is degraded for 6-sector layout. Our proposed network layouts have outperformed known sectorization schemes. Good tradeoff among coverage, capacity and mobility has been reached. Good performances have been achieved for 4  2 IBD-CA VS layout using low frequency band (800 MHz) outer cells. We notice a site throughput gain up to 200% seen against conventional 3GPP case3 sector layout. As future work, we propose to deeply investigate AAS features and handover parameters to reach more optimized HOS QOS in a multi-layer and multi-radio access technology (RAT) networks. Robust self organizing network (SON) algorithms can be implemented and coordinated to automate network HOS and mobility optimization. References [1] Qureshi Rima. Ericsson mobility report; June 2014. . [2] Cisco and/or its affiliates. Cisco visual networking index: global mobile data traffic forecast update, 2013–2018; February 5, 2014. . [3] Wannstrom Jeanette. LTE-advanced; June 2013. . [4] Kumar S, Kovacs IZ, Monghal G, Pedersen KI, Mogensen PE. Performance evaluation of 6-sector-site deployment for downlink UTRAN long term evolution. In: IEEE vehicular technology conference, vol. 2; 2008. p. 703–7. [5] Laiho J, Wacker A, Novosad T. Radio network planning and optimization for UMTS. 2nd ed. England: John Wiley & Sons; 2006. [6] Huang H, Alrabadi O, Daly J, Samardzija D, Tran C, Valenzuela R, Walker S. Increasing throughput in cellular networks with higher-order sectorization. In: Signals, systems and computers (ASILOMAR), conference record of the forty fourth Asilomar. IEEE; 2010. p. 630–5. [7] Lapszow R. Adaptive antenna model with vertical beamforming and horizontal antenna pattern selectivity for 1800 MHz bandwidth. Ph.D. Thesis Warsaw University of Technology. Faculty of Electronics and Information Technology. Warsaw; 2013. p. 1–6. . [8] 3GPP TR 36.942 V10.2.0 (2010–12), 3rd generation partnership project; technical specification group radio access network; Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Frequency (RF) system scenarios (Release 10). [9] Robert J, Li Z. Higher order horizontal sectorisation gains for a real 3GPP/HSPA+ network. In: Proceedings of the 19th IEEE European wireless conference. IEEE; 2013. p. 1–6. [10] Yilmaz O, Hamalainen S, Hamalainen J. System level analysis of vertical sectorization for 3GPP LTE. In: Wireless communication systems. ISWCS 6th international symposium on. IEEE; 2009. p. 453–7. [11] Nguyen HC, Makinen J, Stoermer W. Performance of HSPA vertical sectorization system under semi-deterministic propagation model. In: Proceedings of the 78th IEEE vehicular technology conference. IEEE; 2013. p. 1–5. [12] Athley F, Johansson MN, Nilsson A. Increased sectorization: horizontal or vertical? In: Proceedings of the 78th IEEE vehicular technology conference. IEEE; 2013. p. 1–5. [13] Song Y, Yun X, Nagata S, Chen L. Investigation on elevation beamforming for future LTE-advanced. In: Proceedings of the IEEE international conference on communications workshops (ICC). IEEE; 2013. p. 106–10. [14] 3GPP TR 36.814 V9.0.0 (Release 9). Further advancements for E-UTRA physical layer aspects, 3rd Generation Partnership Project; 2010. [15] Bettstetter C, Hartenstein H, Pérez-Costa X. Stochastic properties of the random waypoint mobility model. ACM/Kluwer Wireless Networks: Special Issue on Modeling and Analysis of Mobile Networks 2004; 10(5): 555–67.

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[16] Wang M, Yang Y, Kazmi M, Larmo A, Pettersson J, Muller W, Timner Y. Handover within 3GPP LTE: design principles and performance. In: Proceedings of the 70th IEEE vehicular technology conference fall. IEEE; 2009. p. 1–5. [17] 3GPP TS 36.133 V9.3.0 (Release 9). Requirements for support of radio resource management, 3rd Generation Partnership Project; 2010. [18] Jansen T, Balan I, Turk J, Moerman I, Kürner T. Handover parameter optimization in LTE self-organizing networks. In: Proceedings of the 72nd IEEE vehicular technology conference fall. IEEE; 2010. p. 1–5. [19] Dimou K, Wang M, Yang Y, Kazmi M, Larmo A, Pettersson J, Muller W, Timner Y. Handover within 3GPP LTE: design principles and performance. In: Proceedings of the 70th IEEE vehicular technology conference fall. IEEE; 2009. p. 1–5. Leila Aissaoui Ferhi Received her engineering and master degree in communications with distinction from Higher School of Communications SUP’COM Tunisia in 2006 and 2008, respectively. She started her PhD in 2014 and her actual interests are focused on 4G/5G radio networks. She is currently 2G/3G/4G radio network manager at Tunisia Telecom operator in Tunisia and a member of Innov’Com Lab, SUP’COM. Kaouthar Sethom Received her engineering and PhD degree in communications with distinction from Higher School of Communications SUP’COM Tunisia in 2002 and 2006 respectively. She is actually professor at Higher School of Information Technology ESTI, Tunisia. Her actual interests are focused on emerging wireless networks, security and cloud systems. She is a member of Innov’Com Lab, SUP’COM. Fethi Choubani Received engineering, master and PhD degrees from National Engineering School of Tunisa, Tunisia in 1987, ENSEEIHT France in 1988 and National Polytechnic Institute of Toulouse France in 1988, respectively. He is actually professor at SUP’COM. His interests are focused on radio frequency components, antennas and electromagnetic compatibility. He has published more than 100 journal and international conference papers. Ridha Bouallegue Received PhD and HDR degrees from the University of Tunis Manar, Tunisia, in 1998 and 2003, respectively. He is currently a professor at National Engineering School of Tunis and SUP’COM, Tunisia. His interests are focused on physical layer of fourth generation wireless networks. He is the author of two book chapters, 75 conference papers, and 15 journal papers.

Please cite this article in press as: Aissaoui Ferhi L et al. Novel radio cellular design improving capacity and mobility performance for advanced cellular networks. Comput Electr Eng (2015), http://dx.doi.org/10.1016/j.compeleceng.2015.07.019