Joint collision resolution and transmit‐power adjustment for Aloha‐type random access

We consider uplink random access for which slotted Aloha has usually been employed with unknown channel conditions. Upon failure of a transmission attempt, a user cannot tell whether the failure was caused by collision with other simultaneously transmitting users or by his use of insufficient transmit power. If a transmission attempt failed due to collision which could have been resolved by retransmission, increasing transmit power would just waste power and, moreover, reduce the other users' chance of successful access. To handle this lack of information on the cause of failure, we propose a novel Cause‐of‐Failure resolution, where the transmit power is increased after a given number of consecutive unsuccessful access attempts when the probability that a given failure is caused by collision becomes sufficiently low. To exploit the thus‐obtained transmit power for the next random access attempt, we also determine the Cause‐of‐Success based on the number of consecutive successful attempts, i.e., whether to (probabilistically) decrease or maintain the current transmit power. This way, users can adjust their transmit power for random access, which we call Auto Power Fallback (APF), considered as an advanced version of the power ramping algorithm. We evaluate APF by modeling analysis and numerical computation based on the slotted Aloha, showing that APF determines a suitable transmit power for uplink random accesses while achieving good performance. Copyright © 2011 John Wiley & Sons, Ltd. We consider uplink random access for which slotted Aloha has usually been employed with unknown channel conditions. To handle this lack of information on the cause of failure , we propose a novel Cause‐of‐Failure resolution, where the transmit power is increased after a given number of consecutive unsuccessful access attempts when the probability that a given failure is caused by collision becomes sufficiently low. Users can adjust their transmit power for random access, which we call Auto Power Fallback (APF), considered as an advanced version of the power ramping algorithm.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96361/1/wcm1105.pd

Protocol-Level Simulations of Massive Medium Access for Machine-Type Communications

In recent years, Machine-Type Communications (MTC) has become one of the most attractive technologies in the area of wireless networking. Different sources are predicting a large grow of smart grid machine-to-machine deployments in several decades, which also means that the total number of wireless devices will increase dramatically. In connection to this problem, the choice of the standard, which will satisfy all the MTC requirements without harming current wireless deployments has become very relevant. Because of these reasons, many companies are proposing to modify one (or several) of the current wireless standard in a way that it will be possible to use for MTC purposes. This will be perfect from point of view of interference problems, because they will be already included in a standard itself. Third Generation Partnership Project (3GPP) Long Term Evolution-Advanced (LTE- A) is one of the most rapidly developing wireless technologies, that seems to be an ideal candidate for future MTC implementation. However, while the capacity of typical LTE-A network should be enough to satisfy traffic demands of large number of MTC devices, the signaling is not ready to face new requirements. In this Thesis, we are considering and partly solving problems, that could occur in LTE-A signaling channels under MTC conditions. Particularly, these are data access mechanisms, which could be realized via Physical Uplink Control Channel (PUCCH) and Physical Random Access Channel (PRACH). Speaking about assessment methods, the research made in this work is based on 2 approaches: simulation and analysis. Both of them are also in details described in the pages of this Thesis. As a conclusion it could be said that PUCCH channel is not suitable for the MTC data access, while PRACH is having problems only in heavily loaded (overloaded) cases and should be slightly modified to face them

Allocation of control resources for machine-to-machine and human-to-human communications over LTE/LTE-A networks

The Internet of Things (IoT) paradigm stands for virtually interconnected objects that are identifiable and equipped with sensing, computing, and communication capabilities. Services and applications over the IoT architecture can take benefit of the long-term evolution (LTE)/LTE-Advanced (LTE-A), cellular networks to support machine-type communication (MTC). Moreover, it is paramount that MTC do not affect the services provided for traditional human-type communication (HTC). Although previous studies have evaluated the impact of the number of MTC devices on the quality of service (QoS) provided to HTC users, none have considered the joint effect of allocation of control resources and the LTE random-access (RA) procedure. In this paper, a novel scheme for resource allocation on the packet downlink (DL) control channel (PDCCH) is introduced. This scheme allows PDCCH scheduling algorithms to consider the resources consumed by the random-access procedure on both control and data channels when prioritizing control messages. Three PDCCH scheduling algorithms considering RA-related control messages are proposed. Moreover, the impact of MTC devices on QoS provisioning to HTC traffic is evaluated. Results derived via simulation show that the proposed PDCCH scheduling algorithms can improve the QoS provisioning and that MTC can strongly impact on QoS provisioning for real-time traffic.The Internet of Things (IoT) paradigm stands for virtually interconnected objects that are identifiable and equipped with sensing, computing, and communication capabilities. Services and applications over the IoT architecture can take benefit of the long-33366377CAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOsem informaçãosem informaçã

Analog baseband circuits for WCDMA direct-conversion receivers

This thesis describes the design and implementation of analog baseband circuits for low-power single-chip WCDMA direct-conversion receivers. The reference radio system throughout the thesis is UTRA/FDD. The analog baseband circuit consists of two similar channels, which contain analog channel-select filters, programmable-gain amplifiers, and circuits that remove DC offsets. The direct-conversion architecture is described and the UTRA/FDD system characteristics are summarized. The UTRA/FDD specifications define the performance requirement for the whole receiver. Therefore, the specifications for the analog baseband circuit are obtained from the receiver requirements through calculations performed by hand. When the power dissipation of an UTRA/FDD direct-conversion receiver is minimized, the design parameters of an all-pole analog channel-select filter and the following Nyquist rate analog-to-digital converter must be considered simultaneously. In this thesis, it is shown that minimum power consumption is achieved with a fifth-order lowpass filter and a 15.36-MS/s Nyquist rate converter that has a 7- or 8-bit resolution. A fifth-order Chebyshev prototype with a passband ripple of 0.01 dB and a −3-dB frequency of 1.92-MHz is adopted in this thesis. The error-vector-magnitude can be significantly reduced by using a first-order 1.4-MHz allpass filter. The selected filter prototype fulfills all selectivity requirements in the analog domain. In this thesis, all the filter implementations use the opamp-RC technique to achieve insensitivity to parasitic capacitances and a high dynamic range. The adopted technique is analyzed in detail. The effect of the finite opamp unity-gain bandwidth on the filter frequency response can be compensated for by using passive methods. Compensation schemes that also track the process and temperature variations have been developed. The opamp-RC technique enables the implementation of low-voltage filters. The design and simulation results of a 1.5-V 2-MHz lowpass filter are discussed. The developed biasing scheme does not use any additional current to achieve the low-voltage operation, unlike the filter topology published previously elsewhere. Methods for removing DC offsets in UTRA/FDD direct-conversion receivers are presented. The minimum areas for cascaded AC couplings and DC-feedback loops are calculated. The distortion of the frequency response of a lowpass filter caused by a DC-feedback loop connected over the filter is calculated and a method for compensating for the distortion is developed. The time constant of an AC coupling can be increased using time-constant multipliers. This enables the implementation of AC couplings with a small silicon area. Novel time-constant multipliers suitable for systems that have a continuous reception, such as UTRA/FDD, are presented. The proposed time-constant multipliers only require one additional amplifier. In an UTRA/FDD direct-conversion receiver, the reception is continuous. In a low-power receiver, the programmable baseband gain must be changed during reception. This may produce large, slowly decaying transients that degrade the receiver performance. The thesis shows that AC-coupling networks and DC-feedback loops can be used to implement programmable-gain amplifiers, which do not produce significant transients when the gain is altered. The principles of operation, the design, and the practical implementation issues of these amplifiers are discussed. New PGA topologies suitable for continuously receiving systems have been developed. The behavior of these circuits in the presence of strong out-of-channel signals is analyzed. The interface between the downconversion mixers and the analog baseband circuit is discussed. The effect of the interface on the receiver noise figure and the trimming of mixer IIP2 are analyzed. The design and implementation of analog baseband circuits and channel-select filters for UTRA/FDD direct-conversion receivers are discussed in five application cases. The first case presents the analog baseband circuit for a chip-set receiver. A channel-select filter that has an improved dynamic range with a smaller supply current is presented next. The third and fifth application cases describe embedded analog baseband circuits for single-chip receivers. In the fifth case, the dual-mode analog baseband circuit of a quad-mode receiver designed for GSM900, DCS1800, PCS1900, and UTRA/FDD cellular systems is described. A new, highly linear low-power transconductor is presented in the fourth application case. The fourth application case also describes a channel-select filter. The filter achieves +99-dBV out-of-channel IIP2, +45-dBV out-of-channel IIP3 and 23-μVRMS input-referred noise with 2.6-mA current from a 2.7-V supply. In the fifth application case, a corresponding performance is achieved in UTRA/FDD mode. The out-of-channel IIP2 values of approximately +100 dBV achieved in this work are the best reported so far. This is also the case with the figure of merits for the analog channel-select filter and analog baseband circuit described in the fourth and fifth application cases, respectively. For equal power dissipation, bandwidth, and filter order, these circuits achieve approximately 10 dB and 15 dB higher spurious-free dynamic ranges, respectively, when compared to implementations that are published elsewhere and have the second best figure of merits.reviewe

Kanavien yhdistämistekniikan suorituskyvyn arviointi edistyneissä LTE-järjestelmissä

Carrier Aggregation (CA) is an essential technology component in LTE-Advanced (LTE-A). CA is capable of combining up to five Long Term Evolution (LTE) carriers to be used for multicarrier transmission in both downlink and uplink. CA provides increased throughputs, additional capacity and possibilities for load balancing. This thesis presents the key features of CA. Furthermore, the results from CA performance measurements are analyzed and presented. The measurements were conducted in live network to evaluate the end-user experience. The objective was to determine whether CA is capable of delivering the performance that could be theoretically expected. The performance was measured in LTE-A radio network using 2x20 MHz bandwidth with 2x2 MIMO configuration and Category 6 User Equipment (UE). Only downlink CA was measured, since uplink CA capable UEs were not commercially available. The performance was evaluated with stationary and mobility measurements. The results indicate that CA is capable of providing the expected performance gain. In good radio conditions the maximum downlink throughput is close to the 300 Mbit/s. Furthermore, CA performs well in poor radio conditions. The performance gain can be more than 100 %, if the additional carrier is on an unused band. In CA, a secondary component carrier is configured for the UE, in addition to the primary carrier. The operation is performed in connected state either after connection setup or radio handover. The delay in secondary carrier addition was measured to evaluate the impact on user experience. The results indicate that the secondary carrier addition after connection setup or handover is sufficiently fast, and do not have an impact to the user experience.Kanavien yhdistäminen (engl. Carrier Aggregation) on oleellinen tekniikka edistyneessä Long Term Evolution järjestelmässä. Sen avulla on mahdollista yhdistää enintään viisi LTE taajuutta käytettäväksi monikanavaiseen ala- ja ylälinkin lähetykseen. CA mahdollistaa aiempaa suuremmat siirtonopeudet, lisää verkon kapasiteettia sekä antaa mahdollisuuden kuormanjakoon eri taajuuksien välillä. Tässä työssä esitellään CA:n keskeiset ominaisuudet. Lisäksi CA:n suorituskykymittauksien tulokset on analysoitu ja esitelty. Mittaukset toteutettiin operaattorin tuotantoverkossa, jotta loppukäyttäjän saamaa kokemusta on mahdollista arvioida. Tavoitteena oli selvittää, pystyykö CA tarjoamaan sellaista suorituskykyä, jota voidaan teorian perusteella odottaa. Suorituskykyä mitattiin LTE-radioverkossa käyttäen 2x20 MHz kaistanleveyttä ja 2x2 MIMO:n kokoonpanoa sekä kategorian 6 päätelaitetta. Mittaukset suoritettiin vain alalinkissä, sillä ylälinkin CA-kykyisiä päätelaitteita ei ollut kaupallisesti saatavilla. Suorituskykyä on arvioitu sekä piste- että mobiliteettimittauksilla. Tulokset osoittavat, että CA pystyy tarjoamaan oletetun suorituskyvyn parannuksen. Hyvissä radio olosuhteissa maksimi datanopeus alalinkissä on lähes 300 Mbit/s. Lisäksi CA toimii hyvin myös huonoissa radio-olosuhteissa. Suorituskyvyn parannus voi olla enemmän kuin 100 %, jos lisätty toinen kanava on vähemmän käytetyllä taajuuskaistalla. CA:ssa toissijainen kanava konfiguroidaan päätelaitteelle ensisijaisen lisäksi. Operaatio suoritetaan yhteystilassa joko yhteyden muodostamisen tai solunvaihdon jälkeen. Toissijaisen kanavan lisäämisen aiheuttama viive mitattiin, jotta sen vaikutus käyttökokemukseen voitiin arvioida. Tulokset osoittavat, että toissijaisen kanavan lisääminen yhteyden muodostamisen tai solunvaihdon jälkeen on riittävän nopea operaatio, eikä sillä ole vaikutusta käyttökokemukseen

Intelligent Resource Allocation in 5G Multi-Radio Heterogeneous Networks

The fast-moving evolution of wireless networks, which started less than three decades ago, has resulted in worldwide connectivity and influenced the development of a global market in all related areas. However, in recent years, the growing user traffic demands have led to the saturation of licensed and unlicensed frequency bands regarding capacity and load-over-time. On the physical layer the used spectrum efficiency is already close to Shannon’s limit; however the traffic demand continues to grow, forcing mobile network operators and equipment manufacturers to evaluate more effective strategies of the wireless medium access.One of these strategies, called cell densification, implies there are a growing number of serving entities, with the appropriate reduction of the per-cell coverage area. However, if implemented blindly, this approach will lead to a significant growth in the average interference level and overhead control signaling, which are both required to allow sufficient user mobility. Furthermore, the interference is also affected by the increasing variety of radio access technologies (RATs) and applications, often deployed without the necessary level of cooperation with technologies that are already in place.To overcome these problems today’s telecommunication standardization groups are trying to collaborate. That is why the recent agenda of the fifth generation wireless networks (5G) includes not only the development schedules for the particular technologies but also implies there should be an expansion of the appropriate interconnection techniques. In this thesis, we describe and evaluate the concept of heterogeneous networks (HetNets), which involve the cooperation between several RATs.In the introductory part, we discuss the set of the problems, related to HetNets, and review the HetNet development process. Moreover, we show the evolution of existing and potential segments of the multi-RAT 5G network, together with the most promising applications, which could be used in future HetNets.Further, in the thesis, we describe the set of key representative scenarios, including three-tier WiFi-LTE multi-RAT deployment, MTC-enabled LTE, and the mmWave-based network. For each of these scenarios, we define a set of unsolved issues and appropriate solutions. For the WiFi-LTE multi-RAT scenario, we develop the framework, enabling intelligent and flexible resource allocation between the involved RATs. For MTC-enabled LTE, we study the effect of massive MTC deployments on the performance of LTE random access procedure and propose some basic methods to improve its efficiency. Finally, for the mmWave scenario, we study the effects of connectivity strategies, human body blockage and antenna array configuration on the overall network performance. Next, we develop a set of validated analytical and simulation-based techniques which allow us to evaluate the performance of proposed solutions. At the end of the introductory part a set of HetNet-related demo activities is demonstrated