Cloud RAN, Radio-over-Fiber: Cloud paradigm for Wireless Networks
Distributed Node-B architecture called Cloud Radio Access Network (C-RAN) is the new paradigm in base stations architecture that aims to reduce the number of cell sites while increasing the base station deployment density bypassing some of the zoning and construction hurdles to brining up new sites on-air. Metro cities like NY, LA and SFO already have a high density of Cell towers. As LTE and more complex wireless technologies are being deployed – would it not make sense to re-use and harness the existing infrastructure?
The concept of the Cloud RAN comes with a new architecture that breaks down the base station into a Base Unit (BU) – a digital unit that implements the MAC PHY and AAS (Antenna Array System) functionality, and the Remote Radio Head (RRH) that obtains the digital (optical) signals, converts digital signals to analog, amplifies the power, and sends the actual transmission. By making the RRH an active unit capable of converting from analog to digital, operators can now place numerous BUs in a single geographical point while distributing the RRUs according to the RF plans. The RRH becomes an intelligent antenna array which not only submits RF signals but also handles the conversion between digital and modular data. New RRH can also support multiple cellular generation (2G, 3G and LTE) eliminating the need for multiple antennas.
The Cloud RAN lowers operating expenses and simplifies the deployment process. By centralizing all the active electronics of multiple cell sites, at one location (aka the “Base Station Server”), energy, real-estate and security costs are minimized. The RRH can be mounted outdoor or indoor – on poles, sides of buildings or anywhere a power and a broadband connection exist, making installation less costly and easier. The RRH is typically connected using fiber to the BU, creating cloud-like radio access network topology. This topology saves costs both during the installation and later on technology upgrades for both software as well as hardware saving the operators millions of dollars in CAPEX/OPEX.
Enablers for Trending towards RAN Clouds
WDM-PON: A passive optical network (PON) is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 16-128. A PON consists of an optical line terminal (OLT) at the service provider’s central office and a number of optical network units (ONUs) near end users. A PON reduces the amount of fiber and central office equipment required compared with point to point architectures. A passive optical network is a form of fiber-optic access network.
Downstream signals are broadcast to all premises sharing a single fiber. Encryption can prevent eavesdropping. Upstream signals are combined using a multiple access protocol, usually time division multiple access (TDMA). The OLTs “range” the ONUs in order to provide time slot assignments for upstream communication.
WDM-PON: Wavelength Division Multiplexing PON, or WDM-PON, is a non-standard type of passive optical networking, being developed by some companies.
The multiple wavelengths of a WDM-PON can be used to separate Optical Network Units (ONUs) into several virtual PONs co-existing on the same physical infrastructure. Alternatively the wavelengths can be used collectively through statistical multiplexing to provide efficient wavelength utilization and lower delays experienced by the ONUs.
There is no common standard for WDM-PON nor any unanimously agreed upon definition of the term. By some definitions WDM-PON is a dedicated wavelength for each ONU. Other more liberal definitions suggest the use of more than one wavelength in any one direction on a PON is WDM-PON. It is difficult to point to an un-biased list of WDM-PON vendors when there is no such unanimous definition. PONs provide higher bandwidth than traditional copper based access networks. WDM-PON has better privacy and better scalability because of each ONU only receives its own wavelength.
CPRI: The Common Public Radio Interface (CPRI) standard defines the interface of base stations between the Radio Equipment Controllers (REC) in the standard, to local or remote radio units, known as RRU or Radio Equipment (RE).The companies working to define the specification include Ericsson AB, Huawei Technologies Co. Ltd, NEC Corporation, Alcatel Lucent and Nokia Siemens Networks GmbH & Co. KG.
The CPRI specification enables flexible and efficient product differentiation for radio base stations and independent technology evolution for Radio Equipment (RE) and Radio Equipment Control (REC).
Scope of Specification: The necessary items for transport, connectivity and control are included in the specification. This includes User Plane data, Control and Management Plane transport mechanisms, and means for synchronization.
A focus has been put on hardware dependent layers (layer 1 and layer 2). This ensures independent technology evolution (on both sides of the interface), with a limited need for hardware adaptation. In addition, product differentiation in terms of functionality, management, and characteristics is not limited. With a clear focus on layer 1 and layer 2 the scope of the CPRI specification is restricted to the link interface only, which is basically a point to point interface. Such a link shall have all the features necessary to enable a simple and robust usage of any given REC/RE network topology, including a direct interconnection of multiport REs. Redundancy mechanisms are not described in the CPRI specification, however all the necessary features to support redundancy, especially in system architectures providing redundant physical interconnections (e.g. rings) are defined.
The specification has the following scope:
1. A digitized and serial internal radio base station interface between ‘Radio Equipment Control’ (REC) and ‘Radio Equipment’ (RE) as well as between two ‘Radio Equipments’ (REs) is specified.
2. Three different information flows (User Plane data, Control and Management Plane data, and Synchronization Plane data) are multiplexed over the interface.
USD database developments
Unified Subscriber Database provides for a single unified view of the subscriber centric data necessary for provisioning applications, engineering subscriber services, and partner subscriber data interactions (through Partner Publisher).
USD Implementation with Data Broker
In order to deliver a personalized mobile experience, service providers need to leverage a key strategic asset – subscriber data. Some of this data is relatively static – for example, a person’s service entitlements, payment method (pre, post, casual), registered devices. Some of this data is more dynamic and is generated by a subscriber’s real time state or behavior – for example, the choices a person makes, their location, and the time of day they use particular services or download new applications to their mobile device. There is also historical usage data for accounting, reporting, or pattern recognition which entails dynamic collection and distribution of large volumes. Often, subscriber data is dispersed throughout the network and sometimes resides within different applications. Capturing it and making use of it is the key to offering better and more personalized services, and as a result, increasing revenues and customer loyalty. Service providers can use subscriber data to offer personalized services such as: Providing a ‘day pass’ for a new service. Delivering more bandwidth to a person who wants to engage in mobile gaming in the evening but not during the day. Allowing a subscriber to download 10 mobile videos per month; or Providing streaming videos or music when you are in one country but not when you are in another because the service provider does not have distribution rights for that location. Providing permission-based subscriber context for targeted advertising.
This is the kind of service personalization that allows service providers to attract and retain subscribers in a competitive market.
Evolution of the Radio Basestation (RRU’s)
The Radio basestation in a Wireless network is the node at the edge of the network communicating with the handset even when the customer is not using the phone. In today’s data-centric world the phone is in an ‘always-on’ mode meaning that the handset is exchanging information with the basestation at all times.
The evolution of the Radio basestation has evolved over the years from the Motorola AMPs equipment to today’s ALU light radio. Today’s deployments happen with various blended models – traditional Basestations as well as Remote Radio Units (RRU) with a distributed basetation architecture where the functions of the Radio and the Baseband are distributed. Here is an older blogpost that I had done on that.
The disruptive architecture of the future will be a blend of the traditional as well as centralized and pooled baseband processing – virtual base stations.
Trends for RAN Clouds Architecture
Shannon Bound Limitations: Communication link rates approach Shannon Bound limit very closely to a capacity of 100 Mbit/s. In information theory, the Shannon–Hartley theorem tells the maximum rate at which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise. It is an application of the noisy channel coding theorem to the archetypal case of a continuous-time analog communications channel subject to Gaussian noise. The theorem establishes Shannon’s channel capacity for such a communication link, a bound on the maximum amount of error-free digital data (that is, information) that can be transmitted with a specified bandwidth in the presence of the noise interference, assuming that the signal power is bounded, and that the Gaussian noise process is characterized by a known power or power spectral density.
Moving Access Closer to the user: As we have experienced the performance comparison between Wi-Fi and the cellular networks, closer the access point and the lesser the number of users the radio link performance increases multi-fold. Adding more radios or adding femtocells increases the user experience and most of the times this differentiates between two different operators.
Cloud Computing capability: 2010 was the biggest year for Cloud computing and the advantages of the cloud have been legendary. As multi-core processors becomes more and more powerful and cloud computing based IT platform are now a popular implementation for traditional IT companies.
Reduced Cost – It helps keep the cost down for both the users and Telco operators. Also for the users, they can access it from any location and still have the capacity they need. For the owners, they do not need to reproduce the hardware and software at every location.
Automatically Updated from a central location Operators no longer need to hire engineers to update more than one location. The server gets the updates and everyone who uses the service gets the updates without updating anything on their end.
Computing Flexibility It has more flexibility than other network computing systems and saves time plus money for people who are in a time crunch.
Mobility Like most networks it allows users to connect even without their own computers, meaning you can do your work from anywhere in the world as long as you have an internet connection and a computer access. So you can take your work with you on your wedding and vacations.
Shared capacity and resources A key component of cloud computing is that companies share resources. With cloud computing, this allows them all to have access to the resources via cloud computing. This again saves MNOs time and money by placing their resources all in one location that is easy for their workers to look up and access.
Cloud RAN Eco-system
When Alcatel-Lucent announced a major collaboration with China Mobile to develop a ‘cloud RAN’, it seemed that Intel’s similar project with the giant carrier might have been shelved. However, it seems China Mobile is exploring multiple routes in its bid to develop the most modern form of LTE network, one that uses huge numbers of compact base stations whose baseband processing is centralized in the cloud. Intel said it is still working on the program, together with an unnamed Chinese vendor.
Like ALU’s lightRadio, the Intel design splits the base station from the integrated antenna/radio at the cell site. The chip giant will provide the cloud computing platform while the anonymous partner – (probably ZTE) which has been getting very close to Intel – develops the compact base stations. As reported by ConnectedPlanet, the survival of the Intel/China Mobile project – first outlined last year – was signaled at the TIA show, where Rose Schooler, general manager of Intel’s Communications Infrastructure Division, pointed to a highly flexible baseband resource that could be weighted towards the sites with highest demand.
ZTE seems the most likely partner because it has announced its own cloud RAN strategy and is working with Intel in other areas such as MeeGo. Huawei has so far taken the line that C-RAN is for the future and it would rather focus on lightweight base stations that are deployable now – and by operators lacking the investment in fiber that C-RAN requires. However, Huawei does partner with Intel on its Single Cloud data center platform. China Mobile is heavily focused on C-RAN, which could provide a logical and cost effective way to upgrade its vast GSM network (700,000 sites) to TD-LTE and do so in a modern and flexible way.
Intel’s activity in this sector indicates how other players may move across from the data center, notably Cisco and IBM. It is adapting a system devised for corporate computing to the needs of telecoms networks. Schooler said this approach would allow telcos to escape from their proprietary interfaces and wide variety of protocols, and work with common platforms to reduce cost and risk.