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Since 1990, wireless communications has rapidly evolved and number of network protocols has increased. Simultaneously, there have been a growth of wireless communication standards such as GSM, IS-95, CDMA UMTS, PHS, and IEEE 802.11. But, the advance in Code Division Multiple Access (CDMA) technology makes it possible for a third generation Mobile Station (MS) to support applications that require high data rates, capacity and multimedia capabilities. Some of existing MSs and more in future are thus devices supporting entertainments capabilities, data and messaging services. To support high quality services and improve the satisfaction of the users, Over the Air (OTA) management of parameters and software resources in a MS would be useful. This the starting point of using OTA which is later extended to more than modifying the contents of SIM cards, provisioning, parameter administration, software downloading, etc to download objects such as a media.OTA is simply depicted in Fig. 1.
Moving from over the internet to OTA, which is the efficient step for Network Operator (NO). Because, OTA enables a NO to introduce new SIM services or to modify the contents of SIM cards in a rapid and cost-effective way. Indeed, that is with the end user agreement and without having to return to a retail outlet.
OTA is based on client/server architecture where at one end there is an operator back-end system (customer care, billing system, application server…etc ) and at the other end there is a SIM card (end user terminal).
Fig. 2 is an example of a basic download implemented by Open Mobile Alliance(OMA), describing the basic functionality provided in OMA Download Over the Air (OMA DLOTA). The user gets a Download Descriptor, downloads a Media Object, and the Status Report Server is notified when the download is complete.
As depicted in Fig. 2, the mechanism of OMA DLOTA as the following :
- While using Discovery Application, the User is typically presented with a reference to the Download Descriptor. The reference may be on a Web page, or inside an email or MMS message, or stored in memory or in an accessory attached to the phone. Content discovery and how to find the URI to the Download Descriptor, is outside the scope of DLOTA.
- The Download Agent selects a URI that points to the Download Descriptor in the DLOTA Server.
- The Download Descriptor is delivered to the Download Agent. The Download Descriptor includes a URI that points to the Media Object.
- The Download Agent analyses the Download Descriptor and checks the capability of device (e.g. available memory size, content type of the Media Object, etc.).
- Using the information included in the Download Descriptor, the Download Agent requests the User to confirm whether to proceed with the download transaction or not.
- The User decides to proceed with the download transaction.
- The Download Agent selects the URI that points to the Media Object and the Download Agent proceeds with the download transaction.
- The Download Agent retrieves the Media Object from the DLOTA Server.
- The Download Agent installs the Media Object.
- The Download Agent successfully reports the status of the download transaction to the DLOTA Server and makes the content available to the User.
In the following sections, the later architectures has been developed are described in section two with illustrating the supporting technology SDR and the methods of downloading delivery. In the third section, it is shown OTA functions and its applications. Wherein, the impact of OTA the faced challenges are explained in section 4. Finally, section 5 concludes the report.
2. architectures and downloading methods
In the first part of this section the generic architectures will be shown as in  and where most of designs are using them as a basic idea. Then, the basic idea of Software defined Radio (SDR) and its principle. In the final parts four method of delivering objects are briefly described.
2.1. General Architecture Schemes
There are two general architectures if we classify them according to downloading source. Whether, the end user downloads from the carrier servers or from other terminals. Following the description of them and comparing of their efficiency.
In small networks one upgrade server might be sufficient to handle upgrading to a view users. Wherein, in large firm many clients are connected, and to avoid overloading situation several downloads server are maintained. Furthermore, load balancing is used to equalize the load over the servers. When, downloading from a main server or N-servers, the design is assumed to be centralized architecture. When a subscriber download from another subscriber without intervention from carrier's server, the architecture said to be decentralized scheme.
2.1.1. Centralized scheme:
Assuming that the end user upgrade takes 2 min and 10 upgrade servers are available. Furthermore, 10 million terminals need to be updated. With sequential updates assuming no multicast, the envisaged total upgrade time calculates to 10 million * 2 min/10 servers = 100,000 h @ 3 yr. Even if we had 1000 network servers (or 10 servers with 100 processors in parallel), the total upgrade time would be 1 mo. With multicast methods, the download time could be further decreased; however, this increases the complexity. In addition, the allocation of network and radio resources increases significantly.
2.1.2. Decentralized scheme:
Assume the terminal upgrade time is 2 min and a perfect snowball system, an exponential growth of the available software upgrade servers can be noticed:
1. cycle 2. cycle 3. cycle 4. cycle 5. cycle 24. cycle
1 terminal 2 terminals 4 terminals 8 terminals 16 terminal 10 million terminals
The total upgrade time is calculated to 2 min * 24 cycles @ 1 h. Terminal-to-terminal upgrades can be realized in HIPERLAN/2 with direct mode, where under the authority of the network two neighbouring terminals can establish a direct link with each other. In a later section a method is proposed to identify a terminal nearby, bearing the required software. Although ideally sketched, a decentralized scheme will offer a dramatic cut down in overall upgrade time, and reduction of allocated network resources and radio resources.
2.2. Software Defined Radio (SDR)
Software-Defined Radio (SDR) is a completely configurable radio that can be programmed in software to define its functionalities. It refers to a technology in which part software modules running on a generic hardware platform consisting of DSPs and general purpose microprocessors are used to implement radio functions such as generation of transmitted signal (modulation) at transmitter and tuning/detection of received radio signal (demodulation) at receiver .
Since 1990, variety of wireless networks standards have been developed which restrained the rapid spread of cellular systems and leads to a problem of constant evolution of link-Layer protocol standards. Therefore, in the fourth generation of mobile communication systems, various technologies will be integrated into a common platform called the Open Wireless Architecture (OWA) where SDR is a key technology that used to implement OWA and helps in dealing with problems due to differing standards.
2.2.1. SDR Features
There are many significant features for the SDR technology, and here are the most common features almost as it mentioned in :
Reconfigurability: while SDR keeps multiple software modules implementing different standards on the same systems, it dynamically configures the system by selecting the proper software to run in the system equipment and end-user device. Wherever, the system equipment can configure itself to user handset.
Ubiquitous Connectivity: SDR enables implementation over the air standards, in which case, networks operators can update their subscriber's handset to match new rolled-out services. That can be much helpful in global roaming facility. Moreover, this feature plays significant role in OTA, precisely, when vendors want to expand their platform to include media over the air.
Interoperability: SDR alleviates designing innovation of open architecture radio system. Wherein, subscribers can seamlessly use third-party innovative application. For instance, Groove Mobile provides mobile music and video as a third-party with telecommunication companies in UK such as THREE, VODAFONE …etc to their subscribers.
2.2.2. SDR Architecture
Before describing the SDR, we will briefly illustrate the basic conventional digital radio system and then we will explain how SDR is involved to implement radio functions in software. However, the radio system consists of four main parts: RF section, analog to digital and digital to analog conversion (ADC/DAC), digital signal processing (DSP) blocks and baseband section, as depicted in Fig. 1.
The front end RF transceiver is the analog part transmitting/receiving radio frequency (RF) via antenna where this antenna should be flexible and reconfigurable to adjust itself with RF module. Also, RF module converts the RF to intermediate frequency (IF) to be processed in ADC/DAC conversion.
To process IF, there is ADC/DAC which is the gate between analog section, RF section, and digital sections, DSP and Baseband sections, by converting the signal from analog to digital and digital to analog. Generally, DSP block is implemented in software as well as baseband operations. In which case, SDR is involved.
Link-layer protocols and modulation/demodulation are implemented by SDR. A combination of evolved hardware component as smart antenna, wideband RF module as well as ADC/DAC conversion and high capacity of DSPs with SDR results in adopted digital radio systems. This system supports multi-band, multi-standards and multi node radio systems.
Generic hardware with programmable modules such as DSPs and analog RF modules are used to implement architecture of software components as it depicted in Fig. 2. Although SDR adds complexity to radio system, it makes the system quit powerful.
Fig. 2 depicts the architecture of software components in a typical SDR system. The system uses a generic hardware platform with programmable modules (DSPs, FPGAs, microprocessors) and analogue RF modules. The operating environment performs hardware resource management activities like allocation of hardware resources to different applications, memory management, interrupt servicing and providing a consistent interface to hardware modules for use by applications. In SDR system, the software modules that implement link-layer protocols and modulation/demodulation operations are called radio applications and these applications provide link-layer services to higher layer communication protocols such as WAP and TCP/IP.
2.3. Download delivery Methods
In this part, we compare pure-push, pure-pull, pull/push and a push/pull approach for component download, all of which use point to point download. We model the process to involve client-side as well as server-side mechanisms. In all of these techniques, when an object component is needed, the end user local cache is searched first. Only if there is a cache miss does the client request a server for the component. The approaches vary in how they handle cache misses.
2.3.1. Pure-Pull Method
This is the most typical scenario where the Download Descriptor and the Media Object are delivered by using a pull method. In this method all bandwidth download dedicated to a pulled pages so there is no periodic push.
2.3.2. Pull-Push Method
The Download Descriptor is delivered by using a pull method, and then the Media Object is delivered by using a push method. In multimedia broadcasting, Media Objects are delivered over a broadcast bearer. This mechanism can be cost effective if the size of the Media Object is large and only limited bandwidth is available.
2.3.3. Push-Pull Method
The Download Descriptor is pushed to the Download Agent, and then the Media Object is delivered by using a pull method. This scenario can used for the situation where the content provider wants to notify the end User that a Media Object is available for download, User, upon reception of the Download Descriptor the User can then decide to download the Media Object using a pull method to download it.
2.3.4. Pure-Push Method
The Download Descriptor and the Media Object are pushed to the Download Agent. This scenario is often used if the network bearer only has a unidirectional bearer. In case of using push, it might be possible to enable unwanted content to be downloaded and installed into a target terminal. For example, a malicious back-end entity may push a Download Descriptor or hide a Download Descriptor behind a hidden hyper-link, thus to trigger the download of a large (and/or malicious) Media Object to the User terminal. In this Method, all bandwidth is dedicated to a periodic push. ,
3. ota functions and applications
In this section, we will discuss the functions of OTA in the first part and its application will be displayed in the second part.
Throughout this decade, various OTA functions are introduced beginning with Over the Air Handset Management (OTAHM) as in  which includes many sub-functions dealing with handset such as Over the Air Parameter Administration (OTAPA), Over the Air Software Download (OTASD) and Over the Air Mobile Diagnostics (OTAMD). Another commercial name, which is brought out by Red Bend Software, is Firmware Over the Air (FOTA). Laterally, these functions are known as Over the Air Programming due to similarity in their functionalities. We will go through the purpose of each one as it is defined with
- OTAHM: it can be classified in to the functions of OTASP, OTAPA, OTASD and OTAMD
- OTASP enables carriers to add new types of services over the air to customer's handset without requiring them to bring their handsets to a network operator location for programming. This makes ease of rolling-out new service. It starts when user manually enters the activation code, which make it optionally, for the selected system.
- OTAPA starts when the network sends OTAPA request command, possibly with user knowledge, with START/STOP bit equal to one. But, it is not allowed if the user-initiated session is in progress, .
With the development of multiple non-converging bearer technologies, the trend is towards an adaptive multi-mode handset, which can switch to the desired bearer, hardware and software configuration on demand . OTASD has techniques for downloading software modules over the air and managing software modules in a handset. Hence it can be categorized as an OTAHM function.
- OTAMD is used to perform diagnostic tests for a handset over the air as well as improving Quality of Service by helping to fix abnormalities in system's network helps.
- Firmware OTA (FOTA)
FOTA provides an integrated and extensible firmware for subscriber's handset which helps network operators, manufacturers and subscribers by easing the mechanism of updating subscriber's handset over the air. Instead of old technique where a cable or is used to update subscriber's handset
- Download OTA (DLOTA)
Instead of downloading any such media object over the Internet to your computer then transfer it to your mobile, DLOTA provides a flexible mechanism for downloading media Objects over the air from network without any limitation of size or type.
In a nutshell, almost all of these functions overlap each other and provide tremendous benefits to the network operators, manufacturers and end user. Moreover, automatic setup within a network and even over global roaming mitigates many problems.
By overlapping the functions mentioned above we can do lots of applications some of these functions support more than one applications even almost all of them such as DLOTA. Following the OTA applications:
- Updating and removing Software.
- Updating and removing Media Objects.
- Download from multiple servers.
- Download of compound objects and multiple objects.
- Download of chunked Media Objects.
- Control of User confirmation prompt.
- Support for resumable download session.
- Authentication of trusted entity and content integrity check
- Downloading by timing reservation.
4. benefites and Challenges
4.1. Benefits of OTA
OTA provide numerous benefits for all of carriers, manufacturers and end user. Most of these benefits are inherent in SDR technology, but are enhanced by OTA software downloads. List of most of them are:
§ Increased customer satisfaction: by providing excellent, quick and even cheap services.
§ Point-of-sale retailers do not need to train staff to undertake activation procedures. It is simple and affective.
§ Operators have number of benefits such as avoiding pre-programming of handsets, reducing the number of resources allocated to service provisioning etc.
§ Increased public safety interoperability: provide the ability of critical emergency response systems or products to work with other systems or products without special effort on the part of the user
§ Reduction in radio lifecycle costs: although the cost of OTA software downloads might be more expensive, these costs could be quickly recovered by savings on operations and upgrade costs. Then, that will be reflected on the end terminal user.
§ Open Platform: OTA enhances open platform which makes third party developers able to innovative application for the end users, which more likely to increase the appeal of the terminal to the end users.
§ Mobile internet: OTA improves IPv6 which in it provides Mobile internet over the air.
4.2. Conducted Works to Assure OTA
OTA has been investigated among many aspects to obtain a good architecture by optimizing existent architectures. Existing works turned to be about the heavy load on the server , reconfigure the hardware components , ,  or reconfigure the software . In this section we will discuss some of the conducted works which tried to assure the OTA quality.
Number of architectures has been proposed to reduce the load from the network operator server. The generic architecture is the centralized scheme with and without load balancing while decentralized scheme proposed to mitigate the load from the server and share with terminals as it discussed in previews section. Software cache server in the base station was introduced to distribute the load with proxy
Moreover, researchers went beyond general design to reconfigure the radio system components such as the reconfigurable antenna with MEMS switches . Also, reconfiguration can be applied by multiplying the number of same component in specific design as it in . Where, four DSP blocks and three pre-post-processors are used to improve the performance of the system.
Digging deeply, many of the works focused on DSR which is used to implement link-layer protocols and modulation/demodulation operations. Starting from , where the basic scenario where suggested (Pure-Push, Pure-Pull and Hybrid Push and Pull). In other work , Assurance Agency is proposed where this agency is responsible for performing software examination and validation.
Recently, OTA is rapidly evolved and involved with downloading aspects all over the network operators and third party who want to use mobile wireless to distribute their objects. OTA is initiated to update software then reconfigured to add and remove, possibly with end user request. With the popularity of media (music and videos) objects and games, all carriers are looking to provide these objects in excellent service to obtain well profits. But, these services demand high bandwidth seamless rolling off.
Coherent and evaluated OTA architectures and reconfigurable SDR mitigate and even solve some problems but still its few of many interesting challenges waiting to be solved. OTA organization is conducting regular free meeting to discuss OTA. OMA had designed their DLOTAv1.0 and optimized it to DLOTAv2.0 to add as many functions as they can.
Providing many applications, need an agency between the servers and end users which need well programmable agency to provide the user with sufficient service. And, assuring that arrival of the objects to the end user still not wholly covered.
Current market drivers such as future-proof equipment, seamless integration of new services, multi-mode equipment and over-the-air feature insertion in commercial wireless networking industry have resulted in widespread interest in SDR technology. The technology can be used to implement wireless network infrastructure equipment as well as wireless handsets, PDAs, wireless modems and other end-user devices. However, factors like higher power consumption, increased complexity of software and possibly higher initial cost of equipment vis-à-vis the benefits offered by the technology should be carefully considered before using SDR technology to build a radio system.
Summarizing, SDR is a promising technology that facilitates development of multi-band, multi-service, multi-standard, multi-feature consumer handsets and future-proof network infrastructure equipment. 
Overall, the impacts of SDR not are as that without OTA downloading which will lead the commercial market upon mobile communication. OTA is the perfect choice instead of downloading over the internet without congestion due to the limitation of internet hardware.
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