Home > Broadband, Femtocell, LTE, WiMAX > Smart RAN for 4G – Compact-BTS, Metro-Femto & ORI

Smart RAN for 4G – Compact-BTS, Metro-Femto & ORI

As we race towards 4G there has been a trend in the radio access network (RAN) architecture of simplifying it, making it more compact and flat. The primary motive has been to enable mobile operators to maintain control on their network costs, while they deal with improving coverage and capacity. However, the explosion in data traffic  volumes, due to smart phones like the iPhone, have thrown a spanner in the works for operators to keep tabs on CAPEX/OPEX costs while they try and keep up with incessantly exploding mobile data demand from burgeoning smart devices, applications, and changing user behavior. This calls for a new architectural paradigm that optimizes existing cell site infrastructure, most of which is macro layer enabled, but at the same time introduces new network layers at the micro-, pico- and femtocell level, that can effectively complement the macro layer.

A new type of base station – the compact BTS along with Femto in the outdoor implementation has also entered the market, further reducing footprint and power consumption, while retaining the performance of macro BTSs. Let us explore these concepts and value proposition that we see for 4G deployment –

  • Compact BTS
  • Metro-Femto
  • ORI – Open Radio Equipment Interface

What is a compact BTS?

It is a single-box base station with radio frequency (RF) and baseband components in a fully integrated, ruggedized enclosure, mounted at the tower top, adjacent to the antenna array, Lightweight equipment with a small footprint, Software-defined, single system-on-a-chip (SoC) architecture. It supports multiple antennas and beamforming with a performance comparable to that of macro BTSs, but with lower power consumption with no ground equipment, shelter, or air conditioning needed. Only power and Ethernet (CAT-5 or fiber) cables are required to operate the base station and connect it to the backhaul.

The compact base station is scalable platforms that can fit into multiple site classifications, ranging from picocell to microcell and macrocell applications. Each site has its own specific equipment characteristics that are required for that specific site. Site-specific classification scheme comes from a set of requirements, such as cell size, max subscribers, total required site capacity, and so forth. These requirements drive the definition of the number capability of a suitable Compact BTS for the type of site, e.g., the RF output power, which is largely determined by site location and targeted cell size. Finally, the capability set then determines suitable Compact BTS specifications, such as type of PA, heat dissipation, physical form factor and so forth.

Traditional macro sites are on rooftops or at a self-supporting site that has a tower mast installed with a cabinet enclosure and is the most common site classification. Macro sites typically have the baseband and radio units enclosed in a cabinet enclosure with the antenna on at the top. This architecture is being transformed with the introduction of remote radio heads (RRH), which combines multiple elements of the RF portion of the base station in a single box. Typical RRH consists of the LNA and the Power Amplifier, TDD Switch or Duplexer, Up and Down Converters, Analog to Digital and Digital to Analog Converters, I/Q Optical Interface, and some degree of OA&M processing. RRH typically supports a single sector and attaches onto the tower mast adjacent to the antenna, and connects to the baseband at the bottom of the tower enclosed in a cabinet connecting with a fiber optic cable. Compact BTS architectures can allow for the RRH to be combined with a baseband processing unit in a single passively cooled unit, eliminating the need for a shelter or cabinet enclosure at the bottom of the tower bringing additional savings on the site and further improving performance.

Metro-Femto and case study of Roke

The pictorial above is the main driver for most operators to go Femto – reduction of churn and Value creation! The reduction in churn contributes favorably to the value created by the basic value proposition. Some operators have reported reductions as high as 50% for FMC propositions similar to femtocells. In reality, after an operator adjusts for the percentage of subscribers adopting femtocells the composite change in churn is modest, although the impact is significant among femtocell users. The impact of churn is greatest driver for any operator as this will drive the bottom line up. Femtocells will now be deployed in the metro areas to ease the traffic offload from macrocells as well to provide indoor solutions.

Femtocells may also be used to serve sparsely-populated rural areas that are conventionally thought of as uneconomic to install a cell phone tower.  Femtocells can now serve as “instant economical infrastructure” to help emergency services or rural residents who are just fed up getting the run around from their local carrier or cell phone tower companies.  Getting the attention of carriers to install new cell phone towers has been the frustration of many wireless customers who live in remote areas.  Femtocells can now provide an economic alternative to ugly and expensive cell phone towers that often require multiple carriers piggybacking upon a new development site.

Roke Manor Research a Siemens’ company has developed a Wide Area Coverage Femtocell capability. Using picoChip’s technology as the development platform, Roke’s reference design has a 40km range which delivers more than many times the area covered by most other femtocells. It is also the first to support full mobility at speeds of up to 120 kilometers per hour, allowing mobile users to travel while connected to the base stations. The femtocell will support up to 12 simultaneous users, with Release 5 HSPA.

Femtocell base stations offer a low cost and low power solution for implementing any network. However, they are only suitable for short range communications of around 200m and as such are ideal for home networks. Roke, however, can now offer all the benefits of a femtocell with an enhanced range of up to 40km. In essence, the Roke modifications permit a macrocell performance in terms of range and mobility within a fetmo hardware platform. Benefits of Roke’s modified femtocell base-station include:

  • Low Power Consumption
  • Range up to 40km
  • Support of 16us Delay Span
  • Mobility up to 120km/hr with  12 users
  • IP Connection to Network
  • Circuit Switched Voice Support

ORI – Open Radio Equipment Interface

In distributed base station architecture the radio base stations consist of a BaseBandUnit (BBU) and a Radio Frequency Unit (RFU), which usually is a Remote Radio Head (RRH). Current interfaces between BBU and RRH are provided in a “semi proprietary” nature, although based on industry standards like CPRI or OBSAI. In order to gain flexibility operators are looking for distributed base station architectures with separate BBUs and RRHs. In order to gain interoperability, BBU and RRH preferably should interconnect via an open BBU-RRH Interface (ORI) for flexible combination from different vendors.

Naturally operator networks are subject to change over time and may require to interface equipment from different vendors too, due to various reasons:

  • Mergers or acquisition of operators with different vendor equipment may cause the necessity to interface equipment from another vendor
  • For flexibility reasons operators may want to interface equipment from different suppliers
  • Termination of a product line from a certain vendor may force an operator to introduce equipment from another vendor

All above cases are assuming, by avoiding replacing the whole equipment chain i.e. BBU&RRH, at least parts of the past investments can be saved.

Due to an open interface between BBU and RRH only those parts need be exchanged subject to a functional/hardware enhancement. As just a limited number of parts need to be exchanged, valuable resources/commodities may be saved too and certain ecological aspects may be claimed additionally. For LTE and utilizing the SON (Self Organizing Networks) capabilities, an open Interface is preferred for plug and play capabilities.

ISG ORI is a direct result of requirements work undertaken by the NGMN Alliance, in their OBRI (Open BBU RRH Interface) project. The ISG is strongly supported by the NGMN Alliance. Leading mobile network operators and telecom equipment vendors have agreed to become founding members of the ISG. The current members and participants of the ISG are: Alcatel-Lucent, AT&T Global Network Services, Deutsche Telekom, DoCoMo Communications Labs Europe, Ericsson, Freescale Semiconductors, Fujitsu Laboratories of Europe, Huawei Technologies, Kathrein-Werke, Motorola, NGMN, Nokia Siemens Networks, NTT DoCoMo, Radiocomp, Reverb Networks, Rohde & Schwarz, Telecom Italia, Ubidyne, Vodafone and ZTE. Other companies are welcome to join the ISG, whose first meeting will took place from 25 to 27 May in Turin, Italy, hosted by Telecom Italia.

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Categories: Broadband, Femtocell, LTE, WiMAX Tags: ,
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